WASHINGTON, D.C. (TNS) — Sen. Jeff Flake warned Sunday that President Donald Trump will face a primary challenge or an independent opponent in 2020 if the Republican continues his bombastic ways.

"I do believe if the president is running for re-election, if he continues on the path that he's on, that that's going to leave a huge swath of voters looking for someone else," Flake, R-Ariz., said on ABC's "This Week." "I think he's inviting that. He's probably inviting a Republican challenge as well."

Flake said he wouldn't rule it out, but that running himself is "not in my plans."

Flake has been critical of the path his party is taking. He pointed to rallies for Trump and other firebrand conservatives, where the audiences are like "spasms of a dying party."

"When you look at the lack of diversity, sometimes, and it depends on where you are, obviously, but by and large, we're appealing to older white men and there are just a limited number of them, and anger and resentment are not a governing philosophy," he said in the interview.

Flake said his faith in the Republican Party was restored when Roy Moore, the party's candidate for the Senate from Alabama, lost a special election this month despite Trump's endorsement.

Flake wrote a $100 check to Moore's Democratic opponent, Doug Jones, and refused to back Moore, who was accused of sexual misconduct with several teenage girls when he was in his 30s.

After Moore's defeat, Flake said, "maybe we can turn back."

"But if we continue to go down that path, just to drill down on the base, I think you'll have a lot of people realize there is no future for them in this party," he said. "I hope, like I said, with the election results in Alabama, that maybe the party's realizing that, we have to change."

Since Trump took office nearly a year ago, Flake has been one of the more critical voices in the president's party.

While Flake said he's willing to work with the president in some instances, he said it's necessary to call Trump out on his questionable statements.

"When we undermine them by talking about alternative facts or talking about statements that are just demonstrably false ... that's just not good, and that's just not right," he said.

But Flake declined to directly answer when asked if he'd call the President a flat-out "liar."

"We can all choose our own words," he said. "And I'd not use that word."