House Speaker Paul Ryan said Friday that his endorsement of Donald Trump is not a "blank check" and acknowledged that he, as well as anyone else he endorses, could ultimately lose his support if they cross the line.

During an interview Friday morning, Milwaukee-based radio host Charlie Sykes asked Ryan if Trump could somehow lose his endorsement, asking if it could happen if Trump were to jump on board with his the idea of kicking Muslims out of the U.S., as suggested by Paul Nehlen, his primary opponent. Ryan told the host that he wouldn't engage in hypothetical questions, but acknowledged that there's a line for everyone he endorses.

"I'm not going to go into the hypotheticals, You and I have had these converstaions." Ryan said. "With any endorsement of anybody, there's never a blank check, and you know that and that's how I've always felt."

The speaker went on to say that he doesn't "see a purpose" in engaging in a "tit-for-tat, petty back-and forth" with Trump because it doesn't help anybody. However, Sykes continued to press, asking Ryan if there is anything that could cause him to withdraw his endorsement.

"But is there an expiration date? Does it ever bounce? Ss there anything that he could say that would cause you to basically say I'm canceling that check," Sykes asked.

"Sure. Of course," Ryan said. "But I'm not going down the road of litigating his past comments.

"Look, when I did end up supporting him after speaking with him [for] a month about our principles, our agenda and what we're trying to achieve and getting agreement on those things, I did say very clearly privately and publicly that if I hear things that I think distort conservatism, that disfigure our principles and values as Republicans, I'm going to speak out and defend ourselves so that people in this country don't get a misperception about who we are and what we believe in, and I've had to do that from time to time — more than I certainly wanted to, like attacking Gold Star parents," Ryan told Sykes.

"Obviously I've done that and I'll continue to do that if necessary. Where that line gets crossed, I don't know where that is — if that is."

The comments come a few days after Trump declined to support him ahead of his primary contest next Tuesday, which Ryan leads by 66 points, according to a new poll. Ryan responded to Trump Thursday, saying that he should focus on Hillary Clinton and not others within the party, calling his decision to do so "strange."