Earlier this month, conservative Washington Post columnist Charles Krauthammer called real estate mogul Donald Trump the “Al Sharpton” of Republican presidential hopefuls. That drew a lot of attention from GOP horse race watchers — and from Trump himself.

Krauthammer revealed that Trump followed up with a phone call challenging him last week, but the Fox News political analyst said he remained unimpressed.

“It didn’t change my view of his un-seriousness as a political candidate one iota,” Krauthammer said on Tuesday’s “The O’Reilly Factor.” “What I did say is that he was gracious and calm on the phone and, given what I’d said about him – that was sort of surprising. So, I gave him credit for that. And also, the fact that he was indicated to me that he was serious about running for the presidency. Because, otherwise, why we call — if he called, why would he be civil?”

Krauthammer mocked Trump’s early presidential platform as bar talk, but host Bill O’Reilly suggested a lot of Americans identify with bar-talk mentality:

KRAUTHAMMER: Look, Bill, that kind of talk is the stuff you expect at a guy at a bar at closing time with slurred speech. That’s not a serious.
O’REILLY: But there are a lot of guys in bars who would support him. Look, I made the analogy yesterday …
KRAUTHAMMER: That’s not a serious presidential candidate.
O’REILLY: In your opinion, but in the guy in the bar, whose vote counts just as much as yours, it is. See, this is the problem we’re getting into. Charles, I made — I made…
KRAUTHAMMER: I don’t have as low an opinion of American people as do you.
O’REILLY: No, I don’t. I’m saying.
KRAUTHAMMER: Is there is anybody out there who thinks that we should seize Iraq oil and we start a war.

Watch:

Regarding the comparison of Trump to Pat Buchanan, who won the New Hampshire Primary in 1996, Krauthammer said Buchanan hadn’t made his entry into politics by running for president.

“No, you’re wrong because the analogy is wrong. Buchanan was a serious guy who had been in politics since the mid-1960s, had worked in the Nixon administration, had worked in the Reagan administration, was familiar and fluent in just about every policy. He was not in any way somebody coming out of the blue and spouting this kind of nonsense.”

And, Krauthammer added, Trump left a lot to be desired on serious issues.

“Look, David Brooks said this morning that the Trump candidacy is semi-crackpot. David is half right,” he said. “Look, I’m not questioning him as a businessman. I’m not questioning him as an honorable American. I’m saying as a politician who aspires to the presidency, this is not a serious candidacy. Yes, he will get some attention here and there. But at the same time when the Republicans aren’t proposing in the Ryan plan a serious attempt to deal with the most serious issue of our time, our debt, we’re deeply engaged in this debate, for us to be speaking about the procedures of the records at the department of births in the department of Honolulu in 1962 is absurd, you know that and I know that.”