In an interview with CNN’s Jake Tapper, Thursday, Republican Speaker of the House Paul Ryan asserted that he cannot, in good conscience, support presumptive nominee Donald Trump.

"I'm just not ready to do that at this point. I'm not there right now,” said Ryan. “Right now, no, there's some work to be done here.”

The announcement reverberated across the Beltway, foreshadowing a potential GOP Civil War in the coming months. Ryan deliberately refrained from using Trump’s name and instead referred to him through an intermediary term: “our presumptive nominee.”

In the last week alone, former presidents George H.W. Bush and George W. Bush have announced that they will not endorse Trump or attend the party’s convention. 2012 GOP presidential nominee Mitt Romney followed suit, refusing to endorse the presumptive nominee. Paul Ryan was Romney’s running mate that election year.

Ryan assumed an optimistic tone on Thursday, implying that he believed there’s a shot that the party may become united. However, that didn’t inspire much confidence from host Jake Tapper, who suggested that party unity may not be possible with such a polarizing figure as the nominee.

Notably, Ryan called for unity 18 times during the interview, according to CNN. “Our presumptive nominee, I believe, needs to unify the party,” Ryan said over and over again, adding:

The bulk of the burden on unifying the party will have to come from our presumptive nominee. don't want to underplay what he accomplished. ... But he also inherits something very special, that's very special to a lot of us. This is the party of Lincoln and Reagan and Jack Kemp. And we don't always nominate a Lincoln or a Reagan every four years, but we hope that our nominee aspires to be Lincoln- or Reagan-esque -- that that person advances the principles of our party and appeals to a wide, vast majority of Americans.

"I'm just not ready to do that at this point."

Paul Ryan, on supporting Donald Trump

Ryan continued:

And so, I think what is necessary to make this work, for this to unify, is to actually take our principles and advance them. And that's what we want to see. Saying we're unified doesn't in and of itself unify us, but actually taking the principles that we all believe in, showing that there's a dedication to those, and running a principled campaign that Republicans can be proud about and that can actually appeal to a majority of Americans -- that, to me, is what it takes to unify this party.

The presumptive nominee needs to run a campaign that the party is proud to stand behind. Republicans need to "have something that they're proud to support and proud to be a part of,” said Ryan. “And we've got a ways to go from here to there.”