Republican presidential nominee Donald Trump is "discrediting conservatism." That's what Bill Kristol said Friday on CNN about the New York businessman and reality-TV star.

In a fiery debate with Trump supporter Kayleigh McEnany, Kristol said that Trump's most recent comments stating Barack Obama was the "founder" of the terrorist group ISIS do a disservice to conservatives who have legitimate arguments about why the president was wrong to pull out of Iraq.

"He is discrediting conservatism. He needs to be separated and severed from conservatism," Kristol said. "And every Republican and conservative who cares about the future of the Republican party and conservatism needs to say now, I really do believe this, needs to say now, 'I'm not with Trump.'"

McEnany countered that the election is a "binary choice" and that if Kristol and other anti-Trump conservatives aren't with Trump, then they're supporting Democrat Hillary Clinton. "If she wins this [election] and appoints liberal justices, we will be asking you why you allowed that to happen."

"I'm happy to take that responsibility compared to your taking the responsibility of supporting a man who is utterly unfit to be president of the United States," Kristol said.