Retiring Sen. Jeff Flake (R-Ariz.) said Sunday that he doesn't think he will run for president in 2020, but added that he believes somebody from the GOP needs to challenge President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE.

Flake, a frequent Trump critic, said on CNN's "State of the Union" that somebody needs to run "to remind Republicans what it means to be conservative, what being a conservative really means and what it means to be decent."

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"I think the future of the party is with people with an optimistic vision moving ahead. I don’t think that will be me. I think there are better candidates out there. But somebody needs to run," he added.

Flake said he would "love to see" Sen. Ben Sasse Benjamin (Ben) Eric SasseTrump says he'll sign order aimed at protecting premature babies in appeal to religious voters Government watchdog recommends creation of White House cyber director position Chamber of Commerce endorses McSally for reelection MORE (R-Neb.) be that candidate. He also mentioned Ohio Gov. John Kasich (R) as a potential primary candidate.

"I think there will be somebody. There needs to be somebody," he said.

Flake previously has left open the door for running for the presidency himself in 2020, telling reporters earlier this month that he hadn't "ruled it out" and hadn't "ruled it in."

"If we're going to be a relevant party in the future then we've got to be a decent party," he said at the time. "This politics of grievance and anger and resentment, you know, you can whip up the base for a cycle or two but it wears thin."

Flake also said Sunday that he believes Arizona is "certainly" winnable for a Democrat in 2020.

“It certainly is," he said. "I think we’ll see the same trends as we’ve seen elsewhere. … You cannot run as someone who is just tied at the hip with the president and win statewide. Voters in Arizona are rejecting that.”