WASHINGTON (Reuters) - Paul Ryan, the top elected Republican, ended a long period of soul-searching and endorsed Donald Trump for president on Thursday, a step toward unifying party loyalists behind the insurgent candidate despite concerns about his candidacy.
Ryan had been a high-profile holdout to supporting Trump for the Nov. 8 presidential election out of concern about the presumptive Republican nominee's bellicose rhetoric and break with party orthodoxy on issues including trade and immigration.
The House of Representatives speaker announced his support in a column for the Janesville Gazette newspaper in his home state of Wisconsin. It surfaced in the middle of a speech by Democratic front-runner Hillary Clinton in which she launched a far-reaching attack on Trump's foreign policy credentials.
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Paul Ryan through his career
Ryan says despite differences, he will vote for Trump in November
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)
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Ryan did not specifically use the word "endorse" in his column, but his spokesman, Brendan Buck, made clear that Ryan's move should be seen as an endorsement.
The speaker had criticized the Republican candidate several times, including Trump's proposal in December to temporarily ban all Muslims from entering the United States because of national security concerns.
The 46-year-old Ryan was the only member of the Republican congressional leadership who had not formally embraced Trump.
In a tweet, Trump responded: "So great to have the endorsement and support of Paul Ryan. We will both be working very hard to Make America Great Again!"
Ryan's backing of Trump could give cover to more reluctant Republicans to get behind the billionaire businessman as their best chance to win the White House.
"I think the endorsement is significant because it shows the falling in line of the establishment Republicans from the top," said Republican strategist Ron Bonjean.
It should also help Trump make the case that he can bring the party together as he girds for a Republican nominating convention in July that many party leaders plan to skip.
It also represents a blow to Republicans who have been trying to organize a third-party bid to give party loyalists who cannot abide Trump someone else to support. The "never Trump" crowd includes 2012 nominee Mitt Romney. Ryan was Romney's vice presidential running mate.
While Ryan's decision could push some Republican leaders off the fence, many holdouts remained, such as two former rivals, former Florida Governor Jeb Bush and U.S. Senator Lindsey Graham of South Carolina. Aides to both said their positions had not changed.
Democratic Senate leader Harry Reid described Ryan's move as "abject surrender," adding: "The GOP is Trump's party now."
'HEAL THE FISSURES'
Ryan met Trump in a high-profile meeting last month and they have since had a number of telephone calls.
"It's no secret that he and I have our differences. I won't pretend otherwise," Ryan wrote. "And when I feel the need to, I'll continue to speak my mind. But the reality is, on the issues that make up our agenda, we have more common ground than disagreement."
Ryan said he and Trump had spoken many times in recent weeks about how, "by focusing on issues that unite Republicans, we can work together to heal the fissures developed through the primary."
"Through these conversations, I feel confident he would help us turn the ideas in this agenda into laws to help improve people's lives. That's why I'll be voting for him this fall," Ryan said.
Announcing he will vote for Trump should make it a bit more comfortable for Ryan to chair the party's nominating convention in Cleveland.
While Ryan's endorsement was significant for Trump, there remain many concerns about him within the party.
Longtime Republican financier Fred Malek drew attention to worries about Trump in a column in the Washington Post on Thursday. He cited Trump's criticism last week of New Mexico's Republican governor, Susana Martinez, considered a rising star in the party with the ability to appeal to Hispanics.
"These attacks on fellow Republicans must stop as we move closer to the general election," Malek wrote.
(Additional reporting by Alana Wise, Emily Stephenson and Richard Cowan; Editing by Peter Cooney)