House Speaker Paul Ryan, top Republican, endorses Donald Trump

U.S. House of Representatives Speaker Paul Ryan endorsed Donald Trump on Thursday, ending an extraordinary public split between the Republican Party's presumptive presidential nominee and the nation's highest-ranking Republican office holder.

"I had friends wishing I wouldn't support him. I had friends wishing I would," Ryan said in an exclusive interview with The Associated Press. "I really didn't feel any pressure, other than my goal is to make sure that we're unified so that we're at full strength in the fall so we can win the election."

The Wisconsin Republican acknowledged he continues to have concerns with Trump's combative style.

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"It is my hope the campaign improves its tone as we go forward and it's all a campaign we can be proud of," Ryan said.

Ryan said the endorsement is not the product of any deal with the billionaire developer. Trump won his endorsement, Ryan said, based on "an understanding of our mutually agreed upon principles." Ryan said he specifically wanted to go over Trump's approach to executive power, judicial appointmentsand his position on abortion.

"Those conversations took some time," Ryan said.

"I feel much more comfortable that he's in the same page with us. Most importantly, it is obvious that Hillary Clinton is not," Ryan said.

Announcement ends standoff with Trump

Ryan ended a weeks-long standoff with Trump minutes before the interview by outlining his support for the New York billionaire in a column published in his hometown newspaper.

Ryan's announcement marks a significant shift for a Republican Party desperately trying to come together ahead of a general election matchup against likely Democratic nominee Hillary Clinton. Some of the Republican Party's best known leaders have vowed not to support Trump, including 2012 Republican presidential nominee Mitt Romney, who had tapped Ryan as his running mate.

Trump acknowledged the move on Twitter, saying, "So great to have the endorsement and support of Paul Ryan."

The day before Ryan's announcement, Romney signalled support for a possible third-party candidate instead of the presumptive Republican nominee.

Ryan shocked the political world last month by refusing to endorse Trump once the real estate mogul became the last major Republican presidential contender still in the race. The pair spoke privately in a series of Washington meetings last month and their campaigns have maintained contact.

Yet as the party's so-called "Never Trump" movement struggled to identify a viable alternative, many believed it was only a matter of time before Ryan fell in line.

"It was basically getting a comfort level of our idea about where the country is headed and where it ought to go," Ryan told AP. "It's more of an understanding of each other and these principles and policies."

'He and I have our differences'

Ryan has embraced reforms to Medicare and Social Security as his signature policy fight on Capitol Hill. Most Republicans in Congress have followed Ryan's lead to reduce the cost of the popular programs that are contributing to the national debt.

Trump has repeatedly promised not to cut the popular programs, echoing a position more commonly adopted by Democrats.

"It's no secret that he and I have our differences. I won't pretend otherwise," Ryan wrote in a column in the Janesville Gazette. "And when I feel the need to, I'll continue to speak my mind."

Ryan's announcement was released as Democratic front-runner Hillary Clinton was delivering a foreign policy speech excoriating Trump's approach.