Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.) slammed President Trump's former national security adviser Michael Flynn in an interview aired Thursday, calling him a "conspiracy theorist" unfit to serve in such an office.

Flake told former U.S. Attorney Preet Bharara on the podcast "Stay Tuned with Preet" that he was generally pleased with Trump's national security team, singling out Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE and Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE for praise.

But Flake promptly denounced Flynn's presence on the National Security Council, panning him as a "conspiracy theorist" and rejecting the notion that he would have voted for him had Flynn needed Senate confirmation.

ADVERTISEMENT

"Michael Flynn didn’t come up for a Senate vote," Flake told Bharara, who was fired from his U.S. attorney position by Trump earlier this year. "I said from the beginning, if that were, I wouldn’t have voted for it, that I thought a conspiracy theorist like that doesn’t belong as head of national security."

Flynn's involvement with Trump — first in his campaign and later in his White House — has been an issue of ongoing controversy. During Trump's White House run, Flynn repeatedly promoted conspiracy-laden websites, particularly those pushing false claims about former Democratic presidential candidate Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE.

Flynn was forced to resign from the White House in February, just 24 days into his tenure, after it was revealed that he lied to Vice President Pence about his conversations with then-Russian Ambassador Sergey Kislyak in the month before Trump took office.

Flake has long spoken critically of Trump, but has stepped up his rhetoric in recent weeks after announcing last month that he would not seek reelection in 2018. In a speech on the Senate floor announcing his decision, Flake delivered a thinly veiled condemnation of Trump and the populist wing of the GOP that carried him to victory in 2016.