For 10 years, Ralph Peters regularly appeared on Fox News to offer military analysis and insight as one of the cable network's reliably conservative commenters. But he quit in March in disgust.

Peters, who announced his departure in a blistering farewell note to his colleagues, followed up on Wednesday with another searing attack, saying that the network created by Rupert Murdoch was "doing a great, grave disservice to our country."

The retired lieutenant colonel in the US Army spoke on CNN in his first television interview since his departure. "With the rise of Donald Trump, Fox did become a destructive propaganda machine," Peters said. "And I don't do propaganda for anyone."

For the decade he worked there, Peters said he believed that Fox News was a necessary and legitimate conservative bulwark in the news media and an outlet for libertarian opinions. But under President Donald Trump, the network shifted rightward, he said.

Its popular prime time hosts, particularly Sean Hannity, started to echo Trump's debunked theories of a "deep state" undermining his administration. They joined the president in steadily attacking the US Justice Department, the FBI and other democratic institutions, Peters said.