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Bill Kristol misses the old Fox News.

The Weekly Standard editor-in-chief was for 10 years a regular guest on the network, but he told CNBC's John Harwood that he felt Fox News took a dramatic turn after former President Barack Obama was re-elected in 2012.

"Fox was always, of course, somewhat conservative," Kristol told Harwood. The problem, Kristol said, is that the network has gone down an ideological rabbit hole. "Seventy-five percent of [their content] seems to be birther-like coverage of different issues," he said, referencing how Fox once covered debunked allegations that Obama was born in Kenya.

A notable perpetrator of this type of coverage, Kristol said, is Fox News host Tucker Carlson, who once worked at the Weekly Standard. Kristol said Carlson was one of the "most gifted" young reporters he'd ever encountered, but lamented that his prime-time show on Fox is "close now to racism, white — I mean, I don't know if it's racism exactly — but ethno-nationalism of some kind."

When Harwood asked if he'd discussed that shift with Carlson, Kristol shook his head "no." Watch the interview below. Kelly O'Meara Morales

Update 11:32 a.m. ET: Carlson responded to Kristol's comments with the following statement: "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. 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."