WASHINGTON, May 5 (Reuters) - The top elected U.S. Republican, Paul Ryan, said on Thursday he was not ready to endorse Donald Trump, a sign of the challenges the party's presumptive presidential nominee faces rallying the Republican establishment behind his White House bid.
Ryan, the speaker of the U.S. House of Representatives, said conservatives wanted to know if Trump shares their values.
"I hope to support our nominee, I hope to support his candidacy fully," Ryan said on CNN. "At this point, I'm just not there right now."
Ryan previously criticized Trump for saying that if he did not win the nomination, his supporters might riot at the Republican National Convention in July.
Other Republicans grappled this week with how robustly to support a candidate who shuns the party line on trade and has upset the party establishment with offensive comments about women and immigrants.
See more of Paul Ryan through his career:
Paul Ryan through his career
Top US House Republican Paul Ryan not ready to endorse Trump
Speaker of the House Denis Hastert (L) administers the oath of office to Rep. Paul Ryan (R) of Wisconsin as his family looks on January 6, 1999 at the start of the 106th Congress. The oath is a recreation as the formal oath is administered to the entire congress as a body on the floor of the House. (photo by Rex Banner)
UNITED STATES - DECEMBER 12: Rep. Paul Ryan, R-Wis., speaks at a news conference in which House Republican leaders called for Permanent Tax Relief. (Photo By Tom Williams/Roll Call/Getty Images)
KRT US NEWS STORY SLUGGED: SOCIALSECURITY-DISCUSSION KRT PHOTOGRAPH BY GEORGE BRIDGES/KRT (April 14) Conversation on Social Security between Rep. Paul Ryan (R-WI), shown, and William Novelli, head of AARP, April 5, 2005 (lde) 2005 (Photo by George Bridges/MCT/MCT via Getty Images)
UNITED STATES - JULY 22: MEDICARE BRIEFING--Rep. Paul Ryan, R-Wisc., speaks at a Cato Institute briefing on Medicare reform in the Rayburn House Office Building. Tom Miller, director of Health Policy Studies at Cato, looks on. (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)
WASHINGTON - SEPTEMBER 24: Rep. Paul Ryan (R-WI) questions Peter Orszag, director of the Congressional Budget Office, during a hearing on Capitol Hill about the impact of recent market turmoil on the federal budget on September 24, 2008 in Washington, DC. Orszag reported that while the impact is currently unknown, it is likely to be substantially less than $700 billion. (Photo by Brendan Hoffman/Getty Images)
WASHINGTON - APRIL 27: House Budget Committee ranking member Rep. Paul Ryan (R-WI) (R) delivers an opening statement during a conference committee meeting with Senate Budget Committee Chairman Kent Conrad (D-ND) (L) and House Budget Committee Chairman John Spratt (D-SC) in the U.S. Capitol April 27, 2009 in Washington, DC. House and Senate lawmakers have already struck a tentative deal on the FY2010 budget resolution and they hope to file a conference report after today's meeting. (Photo by Chip Somodevilla/Getty Images)
WASHINGTON - MARCH 19: (L-R) U.S. House Minority Whip Rep. Eric Cantor (R-VA), Rep. Dave Camp (R-MI) and Rep. Paul Ryan (R-WI) listen during a news conference on the health care legislation March 19, 2010 on Capitol Hill in Washington, DC. The House will vote on the Health Care Reform Legislation on Sunday, March 21. (Photo by Alex Wong/Getty Images)
Representative Paul Ryan, a Republican from Wisconsin and chairman of the House Budget Committee, speaks during a news conference at the U.S. Capitol in Washington, D.C., U.S., on Tuesday, April 5, 2011. U.S. House Republicans today unveiled a plan to overhaul the federal budget and slash the deficit in coming years by about three-quarters, with a $6-trillion cut in spending and 25 percent cap on tax rates. Photographer: Joshua Roberts/Bloomberg via Getty Images
MEET THE PRESS -- Pictured: Rep. Paul Ryan (R-WI) left, and moderator David Gregory, right, appear on 'Meet the Press' in Washington, D.C., Sunday, April 10, 2011. (Photo by William B. Plowman/NBC/NBCU Photo Bank via Getty Images)
MILWAUKEE, WI - APRIL 01: Republican Presidential candidate, former Massachusetts Gov. Mitt Romney (R) jokes with U.S. Rep Paul Ryan (C) (R-WI) during a pancake brunch at Bluemound Gardens on April 1, 2012 in Milwaukee, Wisconsin. With less than a week before the Wisconsin primary, Mitt Romney continues to campaign through the state. (Photo by Justin Sullivan/Getty Images)
WASHINGTON, DC - APRIL 26: House Budget Chairman Rep. Paul Ryan (R-WI) is introduced before speaking about 'America's Enduring Promise,' and the federal budget, in a speech at Georgetown University April 26, 2012 in Washington, DC. During his speech, Ryan said that his proposed budget confronts the nation's growing $15 trillion debt before it impacts future generations of Americans. (Photo by Win McNamee/Getty Images)
NORFOLK, VA - AUGUST 11: Republican presidential candidate, former Massachusetts Gov. Mitt Romney (L) jokes with Rep. Paul Ryan (R-WI) (R) after announcing him as the 'next PRESIDENT of the United States' during an event announcing him as his running mate in front of the USS Wisconsin August 11, 2012 in Norfolk, Virginia. Ryan, a seven term congressman, is Chairman of the House Budget Committee and provides a strong contrast to the Obama administration on fiscal policy. (Photo by Win McNamee/Getty Images)
UNITED STATES - SEPTEMBER 14: Rep. Paul Ryan, R-Wis., Vice Presidential candidate, waves to the crowd after addressing the Values Voter Summit at the Omni Shoreham Hotel in Woodley Park. Photo By Tom Williams/CQ Roll Call)
NEWPORT NEWS, VA - SEPTEMBER 18: Republican vice presidential candidate, U.S. Rep. Paul Ryan (R-WI), pauses as he speaks during a campaign rally at Christopher Newport University September 18, 2012 in Newport News, Virginia. Ryan continued to campaign for the upcoming presidential election. (Photo by Alex Wong/Getty Images)
MIAMI, FL - SEPTEMBER 22: Republican vice presidential candidate, U.S. Rep. Paul Ryan (R-WI) hugs waitress, Lourdes Alcerro, during a campaign stop at Versailles restaurant in the Little Havana neighborhood on September 22, 2012 in Miami, Florida. Ryan continues to campaign for votes across the country. (Photo by Joe Raedle/Getty Images)
Republican presidential candidate Mitt Romney (R) and running-mate Paul Ryan share a laugh as they are introduced at a campaign rally September 25, 2012 at Dayton International Airport in Vandalia, Ohio. AFP PHOTO/Mandel NGAN (Photo credit should read MANDEL NGAN/AFP/GettyImages)
Representative Paul Ryan, a Republican from Wisconsin, arrives at a news conference on Capitol Hill in Washington, D.C., U.S., on Tuesday, Oct. 20, 2015. Ryan said he'd be willing to run for speaker of the U.S. House if Republicans unify behind him now, end leadership crises and let him continue spending time with his family. Photographer: Andrew Harrer/Bloomberg via Getty Images
Representative Paul Ryan, a Republican from Wisconsin and chairman of the House Ways and Means Committee, center right, walks down the steps of the U.S. Capitol building following a vote in Washington, D.C., U.S., on Friday, Oct. 9, 2015. Ryan is under heavy pressure from fellow Republicans to run for U.S. House speaker after a hard-line faction forced Speaker John Boehner to resign and his top lieutenant to drop out of the race. Photographer: Andrew Harrer/Bloomberg via Getty Images
Representative Paul Ryan, a Republican from Wisconsin, walks to a meeting in the basement of the U.S. Capitol in Washington, D.C., U.S., on Tuesday, Oct. 20, 2015. Ryan is set to meet with a group of House conservatives Tuesday as he weighs a potential run to replace Speaker John Boehner under pressure from fellow Republicans. Photographer: Andrew Harrer/Bloomberg via Getty Images
Representative Paul Ryan, a Republican from Wisconsin and chairman of the House Ways and Means Committee, center, talks to the media after walking out of the U.S. Capitol building following a vote in Washington, D.C., U.S., on Friday, Oct. 9, 2015. Ryan is under heavy pressure from fellow Republicans to run for U.S. House speaker after a hard-line faction forced Speaker John Boehner to resign and his top lieutenant to drop out of the race. Photographer: Andrew Harrer/Bloomberg via Getty Images
UNITED STATES - OCTOBER 20 - Rep. Paul Ryan, R-Wis., speaks at a news conference following a House Republican meeting, on Capitol Hill in Washington, Tuesday, Oct. 20, 2015. Ryan is stating that he will run for speaker only if he receives enough GOP support by the end of the week. (Photo By Al Drago/CQ Roll Call)
US Speaker of the House Paul Ryan, Republican of Wisconsin, awaits the arrival of Israeli President Reuven Rivlin for a meeting at the US Capitol in Washington, DC, December 10, 2015. AFP PHOTO / SAUL LOEB / AFP / SAUL LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)
WASHINGTON, DC - DECEMBER 10: House Speaker Paul Ryan (R-WI) holds his weekly press briefing on Capitol Hill on December 10, 2015 in Washington, D.C. Paul Ryan spoke on topics including Donald Trump and the spending bill. (Photo by Allison Shelley/Getty Images)
WASHINGTON, DC - DECEMBER 15: Speaker of the House Paul Ryan, (R-WI) speaks during a Politico interview at the Grand Hyatt on December 15, 2015 in Washington DC. Ryan was interviewed by Politico's Chief White House Correspondent Mike Allen during a Politico Playbook Breakfast. (Photo by Mark Wilson/Getty Images)
U.S. House Speaker Paul Ryan (R-WI) (L) holds ceremonial swearing-in for Representative-elect Ralph Norman (R-SC) on Capitol Hill in Washington, U.S., June 26, 2017. REUTERS/Yuri Gripas
Speaker of the House Paul Ryan (R-WI) speaks after Senate Republicans unveiled their version of legislation that would replace Obamacare on Capitol Hill in Washington, U.S., June 22, 2017. REUTERS/Joshua Roberts
Speaker of the House Paul Ryan introduces his new tax policy at the National Association of Manufacturers Summit in Washington, U.S., June 20, 2017. REUTERS/Aaron P. Bernstein
Speaker of the House Paul Ryan visits members of the Republican team prior to the Congressional Baseball Game at Nationals Park in Washington, U.S., June 15, 2017. REUTERS/Aaron P. Bernstein
U.S. Speaker of the House Paul Ryan speaks to the press about President Donald Trump, former FBI Director James Comey and Russia investigations as Republican Conference Chairman Rep. Cathy McMorris Rodgers (R) looks on after a closed meeting of the Republican leadership of the House of Representatives on Capitol Hill in Washington, U.S. May 17, 2017. REUTERS/Aaron P. Bernstein
Speaker of the House Paul Ryan (R-WI) listens as U.S. President Donald Trump speaks during a meeting with members of the Republican Congressional leadership at the White House in Washington, U.S., June 6, 2017. REUTERS/Joshua Roberts
Discover More Like This
BACK TO SLIDE
Ryan said he hoped the party would be unified by this summer, "but I think a lot of the burden is on the presumptive nominee to do that and so we'll see."
"He won fair and square," Ryan said of Trump, acknowledging his own policy differences with the New York billionaire businessman. He added: "If we don't unify all wings of the party, we're not going to win this election."
Trump's remaining rivals in the Republican race dropped out this week, clearing his path to be picked as the presidential nominee. He will likely face Democratic front-runner Hillary Clinton in the Nov. 8 general election.
(Reporting by Mohammad Zargham and Susan Cornwell; Writing by Eric Walsh; Editing by James Dalgleish)