Former U.S. Sen. Jeff Flake, one of President Trump’s most vocal “Never Trump” critics, is heading to Harvard University.

The Arizona Republican is among six new resident fellows who will join Harvard’s Institute of Politics this fall.

Flake was one of Trump’s most vociferous GOP adversaries in the Senate before leaving office in December after declining to seek reelection in 2018.

Flake has been an outspoken critic of Trump since the 2016 election. He has repeatedly called out Trump, accusing him of “reckless, outrageous and undignified behavior” and saying the president’s use of the terms “fake news” and “enemy of the people” smacked of Soviet dictator Josef Stalin’s propaganda.

Last January, Flake joined CBS News as a contributor and announced that he would not launch a Republican primary challenge of Trump for the 2020 presidential race.

“I have always said that I do hope that there is a Republican who challenges the president in the primary,” Flake told CBS This Morning co-host John Dickerson in January. “I still hope that somebody does, but that somebody won’t be me. I will not be a candidate.”

At an event in New York City last March, Flake answered “yes” when asked if it would be better for a Democrat to beat Trump in 2020 if Trump is the Republican nominee.

“I think that four years is difficult enough to unravel some of the damage that has been done internationally to our role, to our leadership position. We cannot, should not go another four years,” Flake said.

Harvard’s other incoming fellows include LaTosha Brown, co-founder of the Black Voters Matter Fund; Bob Cohn, president of The Atlantic; and Isabel de Saint Malo de Alvarado, a former Panamanian vice president and foreign minister.

The Associated Press contributed to this story.