WASHINGTON -- House Speaker Paul Ryan has limits to what he'll accept from presumptive GOP nominee Donald Trump -- it's just that, apparently, Trump hasn't crossed that line yet.

In a sit-down interview in his ceremonial Capitol Hill office on Thursday, Ryan told The Huffington Post that Trump does not have "a blank check" with his endorsement. "I don't know what that line is," Ryan said, "but right now, I want to make sure that we win the White House."

Ryan originally withheld his endorsement of Trump in early May, citing a desire to have "real unity," not "fake unity," with the likely GOP nominee. Four weeks later, Ryan endorsed.

But the speaker doesn't seem to think he and Trump have found authentic harmony. "It's something that has to be worked at," Ryan said, "and we still got work to do."

He added that unity was difficult to achieve when you have "principles" -- presumably like the ones that say people shouldn't be barred from entering the country on the basis of their religion -- "being violated."

On the topic of Trump's proposed Muslim ban and his statements that he could enact such a policy without Congress, Ryan noted that Republicans were releasing part of their agenda on executive overreach that very day, and, in news that's sure to please Trump, Ryan suggested that he and the House of Representatives were prepared to sue a Republican president if need be.

"I would sue any president that exceeds his or her powers," Ryan said.

It's unclear, however, if Ryan thinks Trump enacting a ban on Muslims entering the country would actually exceed presidential powers. "That's a legal question that there's a good debate about," Ryan said, pointing to the 1952 Immigration and Nationality Act.

Another area where the speaker seems willing to give the president plenty of latitude is on an Authorization for Use of Military Force. Congress has been using the same broadly written AUMF for nearly 15 years to justify military action in the Middle East. Asked if Congress had a moral responsibility to vote on a new authorization, Ryan made it clear that he'd prefer to have a vote, but doesn't think it's necessary.

"I would like to have an AUMF, but I am not going to bring an AUMF to the floor that the president insists upon, which is one that ties the hands of the next president," he said.

Ryan entered the speakership last October promising a more free-flowing debate and open legislative process. But he has confronted a number of the same intra-party dynamics that faced his predecessor, former Speaker John Boehner (R-Ohio).

Still, Ryan said in April that he thought he was doing the job better than Boehner. With continued problems in getting a budget done, however, and with Ryan feeling the need to clamp down on the open process that he once promised, Ryan walked that comment back a bit on Thursday.

"I didn't mean it in that kind of context," he said. "I'm different than Boehner. I'm different than John."

What Ryan said he meant was that his style is "more in keeping with the kind of conference we have right now."

That may be true, but Ryan is going back somewhat on his pledge for a more open House. Whereas Boehner tried to pass appropriations bills under "open rules" -- meaning anyone could offer an amendment -- Ryan is now recommending that the House use "structured rules" for spending bills, meaning GOP leadership decides which amendments get a vote.

Ryan defended that shift as necessary to passing appropriations bills.

"As speaker, our members wanted to have an open rule, so I brought forward an open rule," Ryan said. "Then we watched the Democrats engage in dilatory tactics, not to an advance an issue, but to try and kill bills."

Ryan seems to be referring to an LGBT amendment that was attached to an energy and water spending bill. Democrats and some Republicans support the amendment, which would ensure that people working for government contractors can’t be fired for being lesbian, gay, bisexual or transgender, but enough Republicans oppose the language that they're willing to vote against the entire bill to prevent those provisions from going into law.

Faced with that bind, Ryan is tightening the legislative process, though, he argued, leaders were still allowing dozens of amendments on the floor. "Just not the poison pills that are designed to actually kill the appropriations process," he said.

Ryan, 46, entered the speakership after Boehner made the surprising decision to resign and Majority Leader Kevin McCarthy (R-Calif.) made the even more surprising decision to bow out of the speaker's race. Eventually, Ryan, who seemed to have presidential ambitions even before he was named the 2012 running mate to Mitt Romney, took the job.

With Trump's campaign finally looking like it's imploding, there's been a new round of rumors that someone (read: Paul Ryan) might have a chance to take the GOP nomination through a Republican convention rules committee coup.

But Ryan dismisses the suggestion he might have presidential ambitions at the moment.

"I've passed on it 2012, I passed on it in 2016. If I was that ambitious, I would have run by now," he said. "I have presidential-sized policy ambitions, but I've really yet to have presidential-sized personal ambitions."

And if that answer didn’t sound enough like a politician’s, when pressed, Ryan admits that his decision on the presidency could change in time.

"Maybe it's because the stage and phase in life I am," he said. "I think that's really probably it. The reason I have not been as personally ambitious as my policy ambition is, I think is just because the phase of life I'm in, given the stage and age of my family."

Editor’s note: Donald Trump regularly incites political violence and is a serial liar,rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.