Chris Wallace has said working at Fox News became “increasingly unsustainable” before he jumped ship to CNN last December after almost 20 years with the right-leaning cable channel.

His departure dealt a blow to Fox’s news operation at a time when its opinion side had become preeminent. The veteran journalist’s new show begins on archrival CNN’s streaming service this week and the 74-year-old spoke to the New York Times.

“I’m fine with opinion: conservative opinion, liberal opinion. But when people start to question the truth – ‘Who won the 2020 election? Was January 6 an insurrection?’ – I found that unsustainable,” he told the newspaper.

He added: “Before, I found it was an environment in which I could do my job and feel good about my involvement at Fox. And since November of 2020, that just became unsustainable, increasingly unsustainable as time went on.”

When asked why he didn’t leave Fox News earlier, he said: “I spent a lot of 2021 looking to see if there was a different place for me to do my job.”

And he acknowledged: “Some people might have drawn the line earlier, or at a different point…I think Fox has changed over the course of the last year and a half. But I can certainly understand where somebody would say, ‘Gee, you were a slow learner, Chris’.”

After Donald Trump lost the November 2020 election to Joe Biden, Fox skewed further from news to comment, ending its 7pm nightly broadcast, firing the political editor who had been part of Fox accurately projecting on election night that Trump had lost the crucial state of Arizona and promoting Tucker Carlson, the populist commentator and host who has consistently downplayed the insurrection at the US Capitol on 6 January 2021, by extremist Trump supporters, the New York Times noted.

Carlson and other voices aired by Fox have spent the past four weeks playing down Russia’s invasion of Ukraine, going soft on Putin, and undermining the messages of the invaded country’s sovereignty and the Biden administration and Nato in supporting Ukraine.

“One of the reasons that I left Fox was because I wanted to put all of that behind me,” Wallace said, adding that: “There has not been a moment when I have second-guessed myself about that decision.”

Fox has won praise from the Kremlin earlier this month.