Retiring Sen. Jeff Flake, R-Ariz., said he hopes a fellow Republican challenges President Trump in the 2020 GOP primary in an interview clip released Thursday.

"I do hope that somebody does run in the primary against the president," said Flake. "I fear for the future of the party if we don't remember who we are and what principled conservatism really is. And decency, we've got to get back to it."

Flake told C-SPAN host Steve Scully he found it "disturbing" how Trump's supporters still cheer "lock her up" at his rallies about 2016 Democratic presidential nominee Hillary Clinton.

"This is the president's party right now. No doubt. To win in a Republican primary around the country you have to really embrace the president's policies and condone his behavior. That's the bottom line right now, but it won't always be that way," he added. "It does make me fear that it's going to be a longer process to get out of this than it should be. But we will. We have to. Anger and resentment are not a governing philosophy."

[EXCLUSIVE: President Trump lashes 2020 Democrats: 'Horrible' Cory Booker, 'disgrace' Elizabeth Warren, 'one percent' Joe Biden]

The Arizona lawmaker admitted he wished he could have served another six years in the Senate, but didn't want to be in a position where he had to weigh in Trump's behavior or views.

"I never did warm to the president, in the campaign or as he governed," said Flake. "These days, you not only have to embrace the president, you have to embrace all of his politics and his behavior in order to get through a Republican primary. That was never in the cards for me. I just couldn't do it. I would have liked to have stayed maybe for another term."

Flake also said he wished his party had not followed up Supreme Court Justice Brett Kavanaugh's recent confirmation, which was threatened by allegations of sexual assault, by "spiking the ball in the end zone."

"Just doesn't seem right. Doesn't seem right. This is an impartial referee that we're putting on the court," said Flake. "I thought he gave a magnanimous and appropriate speech at the White House, but the fact that there's even an event to celebrate, with only Republicans there, no Democrats, I just didn't think that that was right. So, I haven't said much about it."

The interview will air Saturday at 10 p.m. ET.