House Speaker Paul Ryan (R-Wis.). (Chip Somodevilla/Getty Images)

Tuesday marks four weeks since Donald Trump won the Indiana Republican primary, forcing fellow presidential candidates Ted Cruz and John Kasich out of the race and earning him the mantle of presumptive Republican nominee. It also marked the beginning of a fascinating pas de deux between Trump and House Speaker Paul D. Ryan, who declared two days later that he was “not ready” to endorse the choice of his party’s voters.

Despite rumblings of an imminent endorsement, Ryan (R-Wis.) continues to withhold his blessing as he moves to assemble a traditionally conservative governing agenda — and as Trump deepens his embrace of populist themes at odds with it.

Peter Wehner — a senior fellow at the Ethics and Public Policy Center, a former policy aide to President George W. Bush and a personal and ideological compatriot of Ryan’s for two decades — spoke with PowerPost about the future of the Trump-Ryan relationship.

PowerPost: A lot of people look at Donald Trump and Paul Ryan and wonder why they’re engaged in this dance: Trump’s a Republican, Ryan’s a Republican — what’s the big deal? They’ll end up shaking hands and everybody’s going to be happy. Is it inevitable that these two men are going to reconcile in the end?

Wehner: I think it’s likely, based on the meeting they had and Ryan’s comments after the meeting, but I don’t think it’s inevitable. Some of the vetting still depends on what Donald Trump says and how he acts, how he conducts himself, the policies that he puts forward. If Ryan endorses Trump, I think it’s going to be a difficult decision for Ryan, and I think anybody who knows Paul Ryan well understands why it would be a difficult thing for him to do.

House Speaker Paul Ryan (R-Wis.) told reporter May 26 that he's seeking "real" unity within the Republican party to help win November's presidential election. Ryan said he'd had a "very productive" phone call with GOP nominee Donald Trump. (Reuters)

Explain that.

Paul Ryan in many ways is the antithesis of Donald Trump; he’s everything that Donald Trump is not. He’s a decent human being. He is a conservative. He is steeped in public policy. He cares about ideas. He’s a person who conducts himself with civility and grace in public life. He doesn’t put down his opponents.

He’s aspirational in his message and philosophy. He’s inclusive. He’s an admirable human being, and Donald Trump is not. If you had told me months ago to name a prominent Republican who is in many ways the antithesis of Donald Trump, Paul Ryan would have been at the top of my list. That doesn’t mean that Ryan in the end won’t support Trump, and I think I understand the reasons that he might, but if he does, I don’t think it’s going to be easy.

Is there any one thing about Donald Trump that most gives Ryan pause about embracing his candidacy?

I don’t think it’s just philosophy, I don’t think it’s just policy, and I don’t think it’s just temperament, but I think it’s all of those things together that makes Trump a pretty toxic mix and very much at odds with Ryan’s view of the world.

Take entitlement reform — Paul Ryan has dedicated his public life to limited government and getting the entire House Republican caucus to back entitlement reform. Donald Trump is not only silent about entitlement reform, he’s an active opponent of it.

And then there’s the cruelty and the crudeness of Donald Trump — the mocking of reporters with physical disabilities, the mocking of POWs, the mocking of women for their looks, the stupid, infantile nicknames.

Then there’s the fact that Donald Trump is the shallowest person to ever run for public office when it comes to knowledge of public policy. The man doesn’t know anything and he has no interest in knowing anything, he has no intellectual curiosity. Someone like Paul Ryan whose life has been about the importance of ideas in politics, that’s got to be a problem.

Donald Trump and Speaker Paul Ryan met on May 12. The result? A lot of cameras, and not much else. (Peter Stevenson/The Washington Post)

You mentioned that there are reasons that he might, in the end, reconcile with Trump. What are those reasons?

My guess is what Ryan is hoping for is that he can tether Donald Trump to a conservative dock precisely because Trump is philosophically adrift at sea and he doesn’t have any knowledge of philosophy or policies or ideas. Ryan might be able, by virtue of his institutional role as speaker of the House, be able to make Trump more conservative than he would otherwise be and mitigate some of his worst tendencies and qualities.

I’m not sure that’s going to happen. I think that the idea that you contain Donald Trump is a wish, not a reality, but I don’t think it’s unreasonable for someone like Paul Ryan to try — and Lord knows it’s in the best interest of the Republican Party and the republic for somebody to try and mitigate the worst aspects of Donald Trump.

If he weren’t speaker of the House right now, how would Ryan be handling this?

That’s a great question, and I don’t know the answer to it. I think he would certainly feel more at liberty not to endorse Trump.

But you know, even if he weren’t speaker, he still would be chairman of the [House] Ways and Means Committee, and he would still be influential, and he might want to use his influence to leverage Trump in the right direction.

Let me ask that a different way: How do you think that Ryan prioritizes his various duties — to his party, to his conservative ideals, to the House as an institution? Do you have a sense of how he tends to manage those when they’re in competition?

I think we’ve seen it. We’ve seen Ryan on several occasions speak out, not directly against Trump, but when Trump refused to distance himself from David Duke, when he made his comments about the ban on Muslims.

We saw it in the speech that Ryan gave to interns where he talked about civility and public discourse; we saw it in this most recent video Ryan’s put out, “The Choice,” where he talked about the importance of ideas and not turning politics into a personality contest.

He’s not capitulating, and he’s still giving voice to his beliefs. But I think he’s doing it carefully. He doesn’t want to turn into me or people like me who are critical of Trump on a nearly daily basis. That wouldn’t be appropriate for him, but he is trying to advocate and stand up for and represent conservatism and his view of politics in a responsible way.

If Ryan doesn’t want to deliver an outright endorsement but also doesn’t want Republican civil war, what does that third way look like?

I think that there can be a tense truce between them, and I think that Ryan can make it clear that while he’s not going to actively oppose Donald Trump for president, he has a different view of politics than Donald Trump.

It’s very important that there be a safe harbor for conservatives, particularly young conservatives now who look up and see Donald Trump and find him to be a repellent figure and wonder what happened to conservatism: “Where do I go? Who are the people I look to? Who are the people who give voice to the convictions that once upon a time almost all Republicans and conservatives shared?”

If Paul Ryan can do that, if he can carve out some non-Trump territory and show that there’s a different way to think about politics, speak about politics and approach politics than the way Donald Trump does, I think that that is all to the good.

What do you think Ryan would consider to be a good outcome for this election, assuming it is Trump versus Hillary Clinton?

I imagine that he believes that Hillary Clinton would be the worst outcome. I’m not of that view. I think that they’re both very problematic, and I think that if Donald Trump is the nominee and certainly if he’s the president, he would not only be an active danger to the republic, but he would do tremendous, durable, long-term damage to the Republican Party and so fundamentally redefine it that many of us that who’ve been a part of the Republican Party for our lives couldn’t in good conscience be part of it.

In terms of Ryan, I don’t know. If he endorses him, he’s obviously saying what he thinks would be best, but probably on some level it’s a pick-your-poison choice. Some of us are politically homeless right now — I don’t think that’s the case with Ryan, and I imagine that at the end of the day he would prefer a Trump presidency to a Clinton presidency.

I’m not sure that he’s right about that, but I’d imagine that’s where he is.

Do you think there’s any doubt that he will remain as speaker in the next Congress?

I don’t think Ryan would leave that job unless he felt like he couldn’t be productive in it. You can make an argument that if Trump were president and Ryan were speaker that Trump is so massively uninterested in public policy and so staggeringly ignorant of it that he’d have to defer to other people — and one of the people that he might have to defer to is Paul Ryan. And if that were the case, that would be better for the country than the alternative.

I don’t think Ryan would feel compelled to resign if Trump becomes president, unless something happens while Trump is president where Ryan in good conscience couldn’t execute his duties. Paul’s a person of conscience, so if he ever got to that point he would act on his conscience, but we’re a long way from that.