Trump officially clinched the GOP nomination this week, but Ryan says there's "no timeline" for when he'll endorse his party's standard-bearer. Florida Sen. Marco Rubio, the former Trump rival who once called him a "con artist," told CNN's Jake Tapper he'd be willing to speak on behalf of the businessman at the Republican National Convention in July.
But Ryan, who shocked the political world by saying he wasn't ready to back Trump earlier this month, is still wrestling with when he'll lock arms with the billionaire businessman.
"What I'm most concerned about is making sure that we actually have real party unity, not pretend party unity," Ryan told reporters on Capitol Hill on Thursday.
As more Republicans jump aboard the Trump train, the speaker risks growing more isolated. His leadership colleagues shrug off questions about why he's holding out and are moving past the divisive primary contest to frame the fall as all about defeating Hillary Clinton.
Ryan advisers say he has no regrets in how he handled the Trump situation. This was a decision he made based on his own "gut," aides say. And he doesn't at this point plan to announce an endorsement of Trump during next week's congressional recess.
But some of his House allies believe that the speaker is in a box. He eventually will have to endorse -- or risk the wrath of the party. Ryan has faced a barrage of questions about his lack of endorsement -- and questions continue to grow over what he's holding out for.
Some of his closest colleagues have begun to notice.
"It's a distraction," one of Ryan's House colleagues said. "I'm not sure what he gets out of it."
Earlier this week, a press briefing with reporters was supposed to focus on the House GOP election-year agenda that he has so carefully crafted. Instead, Ryan and his staff had to push back on press reports suggesting that a Trump endorsement was imminent.
Asked at that briefing what he was waiting for, Ryan said: "I think it's important that we discuss the principles that we all share ... and get some understanding on those."
Ryan, according to his allies on Capitol Hill, is struggling with this decision. They know that he would like Trump to align with their views on key conservative issues -- namely abortion and fiscal matters -- but it's hardly clear whether the unconventional candidate will change his style and tune. Moreover, Ryan has privately expressed alarm at the tone Trump has employed during much of the campaign -- an issue that sources say the two men have discussed. But whether Trump will pull back from his bombast is an open question.
"I think Paul sometimes struggles a little bit -- struggles with his role as the speaker, the perceived role of the speaker," said Rep. Steve Womack, an Arkansas Republican. "And where the lines get a little blurry are about his fundamental beliefs about certain things, which I totally respect."
GOP members on Capitol Hill say the way Ryan will come around is by getting Trump to adopt the detailed blueprint he'll roll out to overhaul the tax code, reform health care, promote economic growth and reduce poverty.
"I think it's a healthy relationship that's developing where they are getting over policy issues, talking about policy --that's what is important to the speaker," Pennsylvania GOP Rep. Lou Barletta, an early Trump supporter, told reporters.
Ryan himself said in December, "Our No. 1 goal for the next year is to put together a complete alternative to the left's agenda."
Womack also told CNN that the process to get on the same page as Trump is just a reflection of Ryan's personality. "This is not surprising to me because Paul Ryan is a thoughtful -- thought to be a wonky kind of guy. With that comes a lot of introspection."
But Trump's appeal so far has been fueled by his simple outsider message, not wonky policy talk. Ryan stresses that his staff and the campaign are now in daily contact, but there's no guarantee that Trump will crib from the agenda for his general election strategy. Plus, Trump's positions on immigration and trade are almost 180 degrees from where Ryan has been.
"They are going to be part of a collaborative process on policy papers, and Mr. Trump will be making final decisions and clearly trade is something that he and Paul Ryan don't agree on," Rep. Chris Collins, a New York Republican who was the first member of Congress to endorse Trump, told CNN recently.
Ryan repeatedly steers clear of the issues where he and Trump disagree, and brushes off questions from reporters on Trump's off-the-cuff comments on the campaign trail.
Instead, his office continues to release highly produced campaign-style videos that show the speaker as hopeful and urging the debate to be about ideas instead of insults. The latest version shows Ryan with college students telling them that leaders need to avoid the "bitterness" in politics. "Leaders need to say: 'Here's my principle, here's my solution.' And let's try and do it in a way that is inclusive, that's optimistic, that's aspirational, that's focusing on solutions," Ryan says in the clip.
Barletta said Trump is patient and won't "strong arm" Ryan.
"It's basically when people are ready to come on board they could come. If they have to stay away he respects that. He knows the importance of having a Republican-controlled Senate so he wants everyone to do their own thing -- what you think is best for you."
Other Republican leaders are giving Ryan time and space, but privately acknowledge that the speaker's endorsement would help at least show some unity headed into the fall campaign. If he doesn't eventually endorse, it would come as a shock to party leaders.
"I think he'll get there," said Senate Majority Whip John Cornyn, Republican of Texas. "I think after a tough primary where people choose other candidates, it's not easy to accept the reality. But the reality is he's the nominee. And I think we'll see people unify behind him as the party's nominee."
Trump's decision to release the names of his Supreme Court picks
went along ways to winning over Ryan, but there is still a ways to go, his allies say. The longer he holds out, the more influence he could presumably have over the direction of Trump's agenda and policy positions. Yet if he continues to wait, Ryan will continue to be dogged by questions, something bound to overshadow his own efforts to keep control of the House.
"I think it will all work out," said Rep. Steve Stivers, Republican of Ohio. "I think everybody has an obligation to come together. "It's not just Paul Ryan. It's Paul Ryan and Donald Trump."