Conservative stalwart Bill Kristol stepped up his attacks on Tucker Carlson, calling his former employee’s Fox News show “close to racism” and “ethno-nationalism of some kind.”

In an interview with CNBC’s John Harwood that aired Thursday, Kristol stopped short of calling Carlson’s primetime show racist, but said the show’s content came close.

“He had always a little touch of Pat Buchananism, I would say, paleo-conservativism,” Kristol said of Carlson. “But that’s very different from what he’s become now.

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“I mean, it is close now to racism, white — I mean, I don’t know if it’s racism exactly — but ethno-nationalism of some kind, let’s call it. A combination of dumbing down, as you said earlier, and stirring people’s emotions in a very unhealthy way.”

Carlson was quick to respond — mostly with befuddlement.

“I’m not even sure what he’s accusing me of. He offers no evidence or examples, just slurs, and then suggests that I’m the demagogue,” Carlson told TheWrap. “Pretty funny. Kristol’s always welcome on my show to explain himself, though I assume he’s too afraid to come. What a shame. It would be revealing.”

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Kristol, once a regular on Fox News, now spends most of his on-air time at NBC-affiliated networks. He said Carlson was typical of a broader and destructive change that has taken place at Fox News since President Obama’s 2012 reelection.

“Now Fox is sort of — 75 percent of it seems to be birther-like coverage of different issues. That’s been, I think, bad,” said Harwood. “And you put that together with the social media and the segmentation of everyone into bubbles, and I think there’s some truth to that criticism.”

Kristol, a conservative icon, founded the influential Weekly Standard and hired a young Tucker Carlson to work on the magazine’s staff years ago.