Calling President Trump's immigration rhetoric "bothersome" and warning that the nation is in "crisis," Republican Sen. Jeff Flake on Sunday again called for a primary challenger to take on the president in 2020.

Speaking to ABC's "This Week," Flake, R-Ariz., who has announced that he will retire in January, said Democrats won't work with Republicans on immigration if Trump keeps deriding them.

“They are on record supporting significant border control,” Flake said, referring to congressional Democrats. “And so, when the president says that and calls them ‘clowns’ and ‘losers,’ how does he expect the Democrats to sit down and work with Republicans on these issues?"

“Words matter, what the president says matters, and he ought to knock that off,” Flake, a frequent Trump critic, added.

TRUMP SAYS 'RED WAVE' NEEDED TO PASS IMMIGRATION BILL OVER 'OBSTRUCTING' DEMOCRATS

Earlier Sunday, Trump called out Democrats -- and previous administrations -- for creating problems at the border.

"Democrats, fix the laws," Trump wrote. "Don’t RESIST. We are doing a far better job than Bush and Obama, but we need strength and security at the Border! Cannot accept all of the people trying to break into our Country. Strong Borders, No Crime!"

And on Friday, Trump said that a "red wave" is needed to pass an immigration bill in Congress, as he accused Democrats of “doing nothing but obstructing.”

The solution, according to Flake, is for another Republican to take down the president.

"I’ve said many times I hope that somebody [runs] in the Republican primary, just to remind Republicans what it means to be conservative or Republican, that we believe in limited government, economic freedom, free trade, immigration," Flake said.

Flake has floated the idea of a primary challenger taking on Trump several times this year, and even pointedly refused to rule out his own run against Trump.

"You can’t, as a Republican these days, [oppose] some of the president’s policies ... and expect to win a Republican primary." — GOP Sen. Jeff Flake

But, Flake conceded, recent congressional primary races have shown that Trump has "unfortunately" redefined the party, making a primary challenge harder than ever.

TRUMP-BASHER MARK SANFORD OUSTED IN KEY PRIMARY RACE

"You can’t, as a Republican these days, [oppose] some of the president’s policies ... and expect to win a Republican primary," Flake said. "That’s the reality and then we’re seeing that played out."

Incumbent Republican South Carolina Rep. Mark Sanford, a frequent Trump critic, was ousted in a primary earlier this month by state Rep. Katie Arrington.

Arrington's shock win, which came after Trump endorsed Arrington and slammed Sanford, was a dramatic rebuke of Sanford's heated "Never Trump"-style rhetoric.