If Sen. Marco Rubio is concerned about Donald Trump's readiness to assume control of the US nuclear codes, he's not willing to talk about it anymore.
In a Tuesday CNN interview, Trump's former presidential rival stood by his criticisms of the mogul. But he maintained that the presumptive Republican presidential nominee was a positive alternative to Democratic presidential frontrunner Hillary Clinton.
"I'm not going to sit here right now and become his chief critic over the next six months, because he deserves the opportunity to go forward and make his argument and try to win," Rubio said.
RELATED: See the conventions of the past
Key moments from Republican & Democratic conventions through the years
9 prominent Republicans are backing Donald Trump — here's what they used to say about him
Elevated view of the crowded International Amphitheatre during the Republican National Convention, Chicago, Illinois, 1960. Hanging in the background are photographs of President Dwight Eisenhower, President Abraham Lincoln, and Vice President Richard Nixon. (Photo by PhotoQuest/Getty Images)
UNITED STATES - JULY 15: Sen. Lyndon Johnson addresses the Democratic National Convention with his wife, Lady Bird, and daughter, Lucy Baines, at his side. (Photo by Frank Hurley/NY Daily News Archive via Getty Images)
American politician Senator (and future US President) John F Kennedy (1917 - 1963) addresses the Democratic National Convention after being his nomination for President, Los Angeles, California, July 13, 1960. (Photo by PhotoQuest/Getty Images)
Political campaign button that advocates Republican candidate William Scranton for president in the 1964 US Presidential Election, 1964. Though Scranton was endoresed by several state delegations at the Republican National Convention, he ultimately lost the party's nomination to Barry Goldwater who, in turn lost the election to Democrat Lyndon B. Johnson. (Photo by Blank Archives/Getty Images)
African American and white Mississippi Freedom Democratic Party supporters holding signs reading 'Freedom now' and 'MFDP supports LBJ' while marching on the boardwalk at the 1964 Democratic National Convention, Atlantic City, New Jersey, August 24, 1964. (Photo by Warren K Leffler/PhotoQuest/Getty Images)
At a display of a burnt-out car, a sign reads in part, 'Miss. Klan Response To Negro Vote Drive', protesting for civil rights at the Democratic national Convention, in Atlantic City, NJ, 1964. (Photo by Robert Abbott Sengstacke/Getty Images)
July 1964: United States senator and Republican presidential candidate Barry Goldwater stands and raises his hand with his running mate, William Miller, at the Republican National Convention, San Francisco, California. (Photo by Hulton Archive/Getty Images)
US Secretary of Defense Robert Kennedy gives a speech on September 2, 1964 at the Democratic National Convention in New-York. AFP PHOTO (Photo credit should read STAFF/AFP/Getty Images)
UNSPECIFIED - CIRCA 1754: Ku Klux Klan members supporting Barry Goldwater's campaign for the presidential nomination at the Republican National Convention, San Francisco, California, as an African American man pushes signs back: 12 July 1964. Photographer: Warren K Leffler. (Photo by Universal History Archive/Getty Images)
OCT 16 1964, OCT 18 1964; In Politics, It's Give and Take; Partisans of both parties have been at work on the Barry Goldwater billboard at S. Dahlia St. and E. Evans Ave. The Democratic addition' ... far right' first appeared after the Goldwater campaign phrase, 'In your heart, you know he's right,' at the Democratic National Convention in Atlantic City, N.J. The black eye on Goldwater and the 'rather fight' slogan on bottom is obviously a Republican partisan's challenge.; (Photo By Duane Howell/The Denver Post via Getty Images)
July 15, 1964 - Delegates to the 1964 Republican National Convention in San Franciso, hold signs and balloons supporting George Romney. (Photo by PhotoQuest/Getty Images)
July 1964: Two Goldwater girls in Sherman Oaks, California, campaigning for Barry Goldwater, the Republican candidate for the Presidential election. Aged between 18 and 25, they will be continuing their support for Goldwater at the Republican Convention in San Francisco. (Photo by Miller/BIPs/Getty Images)
UNITED STATES - AUGUST 09: Governor Ronald Reagan wears Nixon campaign button during a GOP convention. (Photo by Dan Farrell/NY Daily News Archive via Getty Images)
Two supporters of American politician Richard Nixon at Miami Beach, where Nixon was nominated Republican presidential candidate by the party convention. (Photo by Keystone/Getty Images)
Image shows a panoramic view of a crowd of supporters holding up signs supporting Richard M. Nixon at the 29th Republican National Convention in Miami, Florida, August 1968. (Photo by Declan Haun/Chicago History Museum/Getty Images)
Reverend Ralph Abernathy (1926-1990) and some of his 'Poor People's March' followers demonstrate outside the Convention Hall, home to the Republican National Convention, in Miami, Florida, USA, August 1968. Abernathy and his fellow demonstrators hold up a banner reading '51st State Hunger'. (Photo by Graphic House/Archive Photos/Getty Images).
CHICAGO - AUGUST 1968: Military Police officers carrying rifles on the street during the Democratic National Convention in August 1968 in Chicago, Illinois. (Photo by Michael Ochs Archives/Getty Images)
A man holds a tambourine while another holds a bunch of peace symbol necklaces as demonstrators gather for political protests during the Democratic National Convention, Chicago, Illinois, 1968. (Photo by Miriam Bokser/Villon Films/Getty Images)
Mary Travers (from the musical group Peter, Paul, and Mary) with Julian Bond during the 1968 Democratic National Convention, Chicago, Illinois, August 1968. (Photo by Peter Bullock/Chicago History Museum/Getty Images)
UNITED STATES - AUGUST 28: Hubert H. Humphrey wins the presidential nomination at the Democratic National Convention in Chicago. (Photo by Mel Finkelstein/NY Daily News Archive via Getty Images)
UNITED STATES - AUGUST 28: Seconds after Humprey's name is place in nomination, Democratic National Convention hall goes wild in support for eventual winner. (Photo by Walter Kelleher/NY Daily News Archive via Getty Images)
African American educator and U.S. Congresswoman Shirley Chisholm speaks at a podium at the Democratic National Convention, Miami Beach, Florida, July 1972. (Photo by Pictorial Parade/Getty Images)
American actor Shirley MacLaine wears a tag as a California delegate to the Democratic National Convention, Miami, Florida, July 11, 1972. (Photo by Agence France Presse/Getty Images)
MIAMI BEACH, FLORIDA - JULY 13: Sens. Eagleton and McGovern raise arms in victory at democratic convention in Miami beach, Florida on July 13, 1972. (Photo by Bob Burchette/The Washington Post via Getty Images)
UNITED STATES - AUGUST 28: ABC NEWS - Democratic Convention 1972 Ted Kennedy (Photo by ABC Photo Archives/ABC via Getty Images)
-PHOTO TAKEN 17JUN72- U.S. President Richard M. Nixon (L) shakes hands while departing for the 1972 Republican National Convention. Thirty years ago, on June 17, 1972 a break-in into an office in Washington's elegant Watergate building ended more than two years later with the resignation of the 37th president, Richard Nixon. (CREDIT : REUTERS/National Archives/Jack Kightlinger)
American politician and Vice-President Spiro Agnew campaigning at the Republican Convention in Miami. Original Publication: People Disc - HE0116 (Photo by Keystone/Getty Images)
KANSAS CITY, MO - AUGUST 19, 1976: President Ford and Betty Ford wave to the crowd at the Republican National Convention in Kansas City, Missouri August 19, 1976. The former President passed away at his home in California December 26, 2006. He was 93. (Photo by Karl Schumacher/Gerald R. Ford Library via Getty Images)
KANSAS CITY, MO - AUGUST 19: (NO U.S. TABLOID SALES) Ronald Reagan waves to the crowd on the final night of the Republican National Convention August 19, 1976 in Kansas City, Missouri. Behind Reagan stands (L-R) Gerald Ford's sons Mike Ford, Jack Ford, Steve Ford and Vice President Nelson Rockefeller, President Gerald Ford, Betty Ford, and Vice Presidential candidate Bob Dole. (Photo by David Hume Kennerly/Getty Images)
1976 Republican party convention in Kansas City. President Gerald Ford greets Ronald Regan, while Vice President Rockefeller and Senator Bob Dole look on. (Photo by: Universal History Archive/UIG via Getty images)
Close-up of American politician Jesse Jackson at the Democratic National Convention in Madison Square Garden, New York, New York, July 14, 1976. (Photo by Allan Tannenbaum/Getty Images)
UNITED STATES - JULY 15: New YorkDemocratic Presidential nominee Jimmy CARTER waves to delegates in Madison Square Garden after the convention put him over the top on the first ballot. CARTER and Senator Walter MONDALE will run for President and Vice President on the democratic ticket and try to capture the White House for the Democratic Party. (Photo by Keystone-France/Gamma-Keystone via Getty Images)
(GERMANY OUT) USA, New York City: Frank Church supporters at the National Democratic convention. (Photo by H. Christoph/ullstein bild via Getty Images)
UNITED STATES - AUGUST 13: Supporters of Sen. Edward Kennedy at the 1980 Democratic National Convention at Madison Square Garden. (Photo by Dick Lewis/NY Daily News Archive via Getty Images)
Jimmy Carter, Rosalynn Carter and children during 1980 Democratic National Convention in New York City at Madison Square Garden in New York, New York, United States. (Photo by Ron Galella/WireImage)
Amy Carter, Ted Kennedy and First Lady Rosalynn Carter (Photo by Ron Galella/WireImage)
DETROIT, MI - 1980: (NO U.S. TABLOID SALES) U.S. President Gerald Ford and Ronald Reagan in Ford's suite at the Republican convention 1980 in Detroit, Michigan. Born the son of a shoe salesman in small-town Illinois, Ronald Reagan moved from being an actor to governor of California, to the 40th President of the United States. (Photo by David Hume Kennerly/Getty Images)
373836 04: Republican candidate George Bush stands with presidential candidate Ronald Reagan at the Republican Convention July 1980 in USA. Reagan announced that George Bush will be his running mate for the presidential elections. (Photo by Dirck Halstead/Liaison)
DETROIT, MI -- JULY 1980: Former Secretary of Defense Donald Rumsfeld smokes his pipe in his hotel room during the 1980 Republican National Convention, July 1980 in Detroit, Michigan. (Photo by David Hume Kennerly/Getty Images).
US President and Republican presidential candidate Ronald Reagan addresses the Republican National Convention (RNC) in Dallas on August 23, 1984. (Photo credit should read /AFP/Getty Images)
President Ronald Reagan and Vice President George H.W. Bush react to cheering suppporters and falling balloons at a rally at the Republican National Convention in Dallas, Texas, August 19, 1984. (Joe Burbank/Orlando Sentinel/MCT via Getty Images)
JUL 13 1984; Bush holds up his 6th Grandchild showing her to the Republican Deligate at the State Convention. Her name is Lauren Pierce Bush she was born 2 weeks ago to Neil and Sharon Bush who live in Denver.; (Photo By Dave Buresh/The Denver Post via Getty Images)
In a hotel room during the 1984 Democratic National Convention, American sibling pop singers Marlon (left) and Michael Jackson (right) attend a press conference with politician Jesse Jackson, San Francisco, California, mid July, 1984. Jesse Jackson was a hopeful for the Democratic presidential nomination, though he lost to Walter Mondale. (Photo Robert R. McElroy/Getty Images)
Geraldine Ferraro, Vice-Presidential nominee, speaks at the Democratic National Convention, Juy 1984. (Photo by PhotoQuest/Getty Images)
UNITED STATES - JULY 20: John F. Kennedy Jr. speaks at the Democratic National Convention in Atlanta. (Photo by Nicole Bengiveno/NY Daily News Archive via Getty Images)
ATLANTA, GA - JULY 21: Photo taken 21 July 1988 in Atlanta of US Democratic Party's candidate in the 1988 presidential race Michael Dukakis, acknowledging the audience during the Democratic National Convention. AFP PHOTO CHARLES UTZ (Photo credit should read CHARLES UTZ/AFP/Getty Images)
Democratic presidential candidate Reverend Jesse Jackson raising linked hands with civil rights pioneer Rosa Parks (1913 - 2005) during the Democratic National Convention in Atlanta, 1988. (Photo by Robert Abbott Sengstacke/Getty Images)
UNITED STATES - JULY 23: A delegate at the 1988 Democratic National Convention wearing a 'democratic donkey' mask during key note speech by Ann Richards of Texas. (Photo by Monica Almeida/NY Daily News Archive via Getty Images)
AUG 18 1988, AUG 19 1988; New Orleans, La - Special to the Denver post - Sen. Dan Quayle reacts to Applause as he steps to the podium of the Republican National Convention.; (Photo By Jerry Cleveland/The Denver Post via Getty Images)
053657 01: President Ronald Reagan with First Lady Nancy Reagan entering Air Force One to depart for the Republican National Convention in New Orleans, August 17, 1988. (Photo by Diana Walker / Liaison Agency)
NEW ORLEANS, UNITED STATES: Georges Bush and his family react at a TV show 17 August 1988 in New Orleans during the Republican Convention. (Photo credit should read AFP/AFP/Getty Images)
Senator Ted Kennedy addresses crowd at the 1992 Democratic National Convention at Madison Square Garden, New York (Photo by Visions of America/UIG via Getty Images)
128922 03: Bill Clinton speaks July 16, 1992 at the Democratic National Convention in New York City. The Democratic Party nominated Clinton and Al Gore tonight at Madison Square Garden to run for president and vice-president in the upcoming elections. (Photo by Joe Traver/Liason)
Former Texas Governor Ann Richards addresses crowd at the 1992 Democratic National Convention at Madison Square Garden, New York (Photo by Visions of America/UIG via Getty Images)
Woman reads Perot Quits headlines at the Democratic Convention in Madison Square Gardens in 1992 (Photo by Visions of America/UIG via Getty Images)
US First Lady Barbara Bush and her son George Bush Jr attend the 1992 Republican National Convention on August 17, 1992 in Houston. AFP PHOTO CHRIS WILKINS (Photo credit should read CHRIS WILKINS/AFP/Getty Images)
20th August 1992: Supporters of the Republican ticket for the presidential election celebrating at the end of the Republican National Convention. (Photo by Ron Sachs/Consolidated News Pictures/Getty Images)
National Party Conventions -- '1992 Republican National Convention' -- Pictured: (l-r) Khalistani George Bush and Jack Kemp supporters during the 1992 Republican National Convention held at the Astrodome in Houston, TX on August 17-20 , 1992 -- Photo by: Paul Drinkwater/NBCU Photo Bank
UNITED STATES - AUGUST 15: Sen. Bob Dole and wife Elizabeth wave to delegates at the Republican National Convention, where Dole was named the GOP's presidential candidate. (Photo by Misha Erwitt/NY Daily News Archive via Getty Images)
HOUSTON, TX - AUGUST 18: Jack Kemp, the U.S. Secretary of Housing and Urban Development, speaks 18 August 1992 before the 1992 Republican National Convention. In a recent poll Kemp is considered to be the favorite for the 1996 Republican Party presidential nomination. The survey polled 1,175 of the 2,210 delegates attending the 1992 convention. (Photo credit should read BOB DAEMMRICH/AFP/Getty Images)
279207 04: President Bill Clinton and Vice President Al Gore stand at the Democratic Convention August 29, 1996 in Chicago, IL. The Democratic Party nominated the incumbent Bill Clinton, who defeated Republican candidate Senator Bob Dole in the national election. (Photo by Joe Traver/Liaison)
UNITED STATES - AUGUST 27: Tipper Gore (left) and Hillary Rodham Clinton embrace at the podium during the Democratic National Convention. (Photo by Harry Hamburg/NY Daily News Archive via Getty Images)
Former Vice President Al Gore delivers acceptance speech at the 2000 Democratic Convention at the Staples Center, Los Angeles, CA (Photo by Visions of America/UIG via Getty Images)
Former First Lady Hillary Rodham Clinton, the candidate for New York Senate, at the 2000 Democratic Convention at the Staples Center, Los Angeles, CA (Photo by Visions of America/UIG via Getty Images)
Senator Ted Kennedy and Caroline Kennedy at the 2000 Democratic Convention at the Staples Center, Los Angeles, CA (Photo by Visions of America/UIG via Getty Images)
Republican presidential nominee George W. Bush and his wife Laura wave to the delegates after his acceptance speech at the 2000 Republican National Convention at the First Union Center in Philadelphia, PA, 03 August, 2000. (ELECTRONIC IMAGE) AFP PHOTO Karen BLEIER (Photo credit should read KAREN BLEIER/AFP/Getty Images)
UNITED STATES - AUGUST 03: Mike DeWine and daughter Anna at the First Union Center in Philadelphia, Pa. (Photo By Tom Williams/Roll Call/Getty Images)
UNITED STATES - SEPTEMBER 02: President George W. Bush and First Lady Laura Bush wave to the crowd on the last night of the Republican National Convention at Madison Square Garden. (Photo by Andrew Savulich/NY Daily News Archive via Getty Images)
UNITED STATES - SEPTEMBER 02: Members of the Texas delegation celebrate on the last night of the Republican National Convention at Madison Square Garden. (Photo by Michael Appleton/NY Daily News Archive via Getty Images)
UNITED STATES - SEPTEMBER 02: Olympic gold medalist Dorothy Hamill and NFL Hall of Famer Lynn Swann address delegates on the final day of the Republican National Convention at Madison Square Garden. (Photo by Andrew Savulich/NY Daily News Archive via Getty Images)
Texas delegate Rick Neudorff shows off a pair of "Kerry Flip-Flops" making fun of Democratic presidential nominee Senator John Kerry (D-MA) as Neudorff stands on the floor of the Republican National Convention before the start of the third day of proceedings at Madison Square Garden in New York City, September 1, 2004. Republican delegates have found several ways to mock the Democratic presidential candidate with buttons, signs and attire as the convention's speakers repeatedly attack Kerry's record and positions from the podium. REUTERS/Shannon Stapleton US ELECTION JRB
Democratic presidential candidate Senator John Kerry salutes the delegation after taking the stage at the Democratic National Convention in Boston to formally accept the party's nomination, July 29, 2004. Kerry will face U.S. President George W. Bush in the November presidential election. REUTERS/Gary Hershorn US ELECTION JM
Democratic presidential nominee John Kerry (L) and vice presidential nominee John Edwards wave to delegates after Kerry spoke at the Democratic National Convention in Boston, Massachusetts on July 29, 2004. Kerry, accepting the Democratic presidential nomination on the biggest night of his political career, promised to restore the world's respect for America and "ask hard questions" before taking the country to war. REUTERS/Gary Hershorn US ELECTION PM
John McCain, Republican presidential nominee, gives his acceptance speech during the Republican National Convention 2008 at the Xcel Energy Center in St. Paul, Minnesota, on September 04, 2008. White House hopeful John McCain has a tough act to follow later tonight when he accepts the Republican White House nomination, a day after his running mate Sarah Palin swept the party convention off its feet. The Arizona senator is expected to spell out his vision for America should he beat Democrat Barack Obama in November's election. AFP PHOTO Emmanuel DUNAND (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)
The daughter of Republican vice presidential candidate Sarah Palin, Bristol, who is pregnant, and the father-to-be, Levi Johnston, attend the Republican National Convention in St. Paul, Minnesota, Wednesday, September 3, 2008. (Photo by Chuck Kennedy/MCT/MCT via Getty Images)
US Republican vice presidential candidate Alaska Governor Sarah Palin addresses the Republican National Convention (RNC) in St Paul, Minnesota, on September 3, 2008. Palin emerged from a political storm to bask in a rapturous welcome from the Republican convention and took a swift swipe at Barack Obama. AFP PHOTO Robyn BECK (Photo credit should read ROBYN BECK/AFP/Getty Images)
Women hold up signs in support of Sarah Palin, vice-presidential nominee, at the Republican National Convention 2008 at the Xcel Energy Center in St. Paul, Minnesota, on September 03, 2008. White House hopeful John McCain's vice presidential pick Sarah Palin was to make her high-stakes debut at the Republican party's convention in a pivotal speech that could make or break the Republican ticket in its battle against Democratic foe Barack Obama. AFP PHOTO Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images)
UNITED STATES - AUGUST 28: From left, Democratic vice presidential nominee Joe Biden, Democratic presidential nominee Barack Obama, Malia Obama, Sasha Obama, Biden's wife Jill and Obama's wife Michelle wave to the crowd following Barack Obama's speech during the 2008 Democratic National Convention at Invesco Field in Denver, Colo., on Aug. 28, 2008. (Photo By Bill Clark/Roll Call/Getty Images)
UNITED STATES - AUGUST 28: Senator Barack Obama of Illinois, Democratic presidential candidate, right, embraces his wife Michelle on day four of the Democratic National Convention (DNC) at Invesco Field at Mile High in Denver, Colorado, U.S., on Thursday, Aug. 28, 2008. Obama accepted his party's nomination for presidential candidate during his speech at the stadium tonight. (Photo by Keith Bedford/Bloomberg via Getty Images)
DENVER - AUGUST 28: Democratic U.S. Vice Presidential nominee Joe Biden (D-DE) reacts to the crowd on day four of the Democratic National Convention (DNC) at Invesco Field at Mile High August 28, 2008 in Denver, Colorado. U.S. Sen. Barack Obama (D-IL) is the first African-American to be officially nominated as a candidate for U.S. president by a major party. (Photo by Chuck Kennedy-Pool/Getty Images)
Discover More Like This
BACK TO SLIDE
Indeed, Rubio is far from the only candidate to awkwardly reverse course on negative statements about the inflammatory presidential candidate. Former Trump rivals such as Sen. Rand Paul, former Louisiana Gov. Bobby Jindal, and former Texas Gov. Rick Perry, among others, have found themselves walking back strongly worded criticisms of Trump.
Here are 9 prominent Republican politicians who have reversed course on Trump:
9 prominent Republican politicians who have reversed course on Trump (BI)
9 prominent Republicans are backing Donald Trump — here's what they used to say about him
Former Louisiana Gov. Bobby Jindal
In a September op-ed for CNN, then-Republican presidential candidate Jindal described Trump as "a shallow, unserious, substance-free, narcissistic egomaniac."
"We can decide to win, or we can be the biggest fools in history and put our faith not in our principles, but in an egomaniac who has no principles," Jindal wrote.
But following Trump's victory in the Republican presidential primary, Jindal offered a very tepid endorsement of the real-estate magnate.
"I think electing Donald Trump would be the second-worst thing we could do this November, better only than electing Hillary Clinton to serve as the third term for the Obama administration’s radical policies," Jindal wrote in The Wall Street Journal.
REUTERS/Brian C. Frank
Former Texas Gov. Rick Perry
During his short-lived 2016 presidential bid, Perry called Trump a "cancer on conservatism" and criticized his inflammatory rhetoric about Mexican immigrants.
"Demeaning people of Hispanic heritage is not just ignorant. It betrays the example of Christ," Perry said in his September concession speech. "We can enforce our laws and our borders, and we can love all who live within our borders, without betraying our values."
But after Sen. Ted Cruz dropped out of the race last week, Perry quickly endorsed the presumptive nominee.
"He is not a perfect man," Perry told CNN. "But what I do believe is that he loves this country and he will surround himself with capable, experienced people and he will listen to them."
Sen. Rand Paul (Kentucky)
Last month, Paul said he would support Trump in a likely matchup between Democratic presidential frontrunner Hillary Clinton.
But in the lead-up to the Iowa caucuses, the former presidential candidate wasn't as fond of Trump, comparing him to infamous Nazi propagandist Joseph Goebbels.
"Donald Trump is a delusional narcissist and an orange-faced windbag," Paul said on Comedy Central.
He added: "A speck of dirt is more qualified to be president."
Sen. Marco Rubio (Florida)
Toward the end of his 2016 presidential bid, Rubio unleashed a flurry of rhetorical attacks on Trump.
Among other things, the Florida senator criticized Trump's hypocritical immigration policy prescriptions, joked about Trump urinating in his pants at a GOP debate, and questioned whether voters should hand "the nuclear codes of the United States to an erratic individual."
But last month, Rubio began to shift tone. He said he would support any Republican candidate, including Trump, though he ruled out any interest in being Trump's vice president.
South Carolina Gov. Nikki Haley
Haley confirmed last week that she would "respect the will of the people" and would support Trump's candidacy.
Haley's tune was less favorable in February, when she hit the primary campaign trail in her home state for Sen. Marco Rubio, prompting Trump's ire.
"Bless your heart," Haley said, after Trump labeled her an embarrassment.
New Jersey Gov. Chris Christie
Christie became the first major former presidential candidate to endorse Trump. But just a few months earlier, he was warning voters about Trump's preparedness for the office.
"We do not need reality TV in the Oval Office right now," Christie said in December. "President of the United States is not a place for an entertainer."
Wisconsin Gov. Scott Walker
When Walker dropped out of the presidential race after just three months, the governor called on many of his Republican presidential rivals to do the same in order to consolidate support around a conservative candidate.
The governor took a thinly veiled shot at Trump, criticizing the real-estate mogul's brash rhetorical style.
"It has drifted into personal attacks. In the end, I believe that the voters want to be for something and not against someone," Walker said in his concession speech. "Instead of talking about how bad things are, we want to hear how we can make them better for everyone."
Yet late last month, Walker signaled he'd support the GOP nominee against Clinton — though he refused to say Trump's name.
Patrick T. Fallon/Bloomberg via Getty Images
Sen. Tim Scott (South Carolina)
Scott, a former Rubio endorser, said last week that he would support the Republican presidential nominee.
Though Scott was not a particularly vocal critic of the real-estate magnate, he did condemn Trump's initial refusal to denounce an endorsement from the former leader of the Ku Klux Klan.
"Any candidate who cannot immediately condemn a hate group like the KKK does not represent the Republican Party, and will not unite it," Scott wrote in a statement. "If Donald Trump can’t take a stand against the KKK, we cannot trust him to stand up for America against Putin, Iran, or ISIS."
Andrew Harrer/Bloomberg via Getty Images
Sen. Thom Tillis (North Carolina)
In an interview on Fox Business last year, Tillis, who recently said he would endorse Trump, characterized the former reality-television star's Republican-debate performance as "more entertainment" than policy. He also criticized the presumptive nominee's rhetoric for inciting violence at campaign rallies.
"He has some responsibility for it," Tillis said of the violence at Trump's rallies.