WASHINGTON – Retiring Arizona Sen. Jeff Flake​ on Sunday wouldn’t​ rule out a 2020 run against President Trump, saying the commander-in-chief is “inviting” a challenger with his politics of division and narrow appeal to a diminishing base of older, white men.

“I don’t rule anything out, but it’s not in my plans,” Flake​, a Republican,​ told ABC’s “This Week.”

“But I do believe if the president is running for reelection, if he continues on the path that he’s on, that that’s going to leave a huge swath of voters looking for something else.”

Flake said he expects Trump could have challengers from multiple sides: Democrat, independent and even from his own Republican Party.

“I think he’s inviting that,” Flake said.

Flake has often clashed with Trump over his incendiary tweets, immigration policies and endorsements.

He most recently wrote a campaign contribution check to Alabama Democrat Doug Jones after Trump backed accused child molester Roy Moore for ​the ​Senate.

Flake said he worries the GOP und​er ​Trump represents “spasms of a dying party.”

“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,” Flake said.

Facing a tough reelection in Arizona and public rebukes from Trump, Flake announced his retirement in a stunning Senate floor speech Oct. 24 that was viewed as a condemnation of Trump’s leadership.

“I will not be complicit,” he said.

If Democrats nominate someone like far-left Sens. Elizabeth Warren or Bernie Sanders in 2020 to challenge Trump, Americans likely will be looking for third option, Flake said.

“That leaves a huge swath of voters in the middle, that may be looking for something else,” he said.