Sen. Jeff Flake (R-Ariz.) said Republicans in Congress need to push back harder on President Donald Trump's criticisms of Russia investigation. | John Shinkle/POLITICO Flake won’t rule out White House run against Trump

Sen. Jeff Flake said Sunday he hasn’t ruled out a challenge to President Donald Trump in the 2020 presidential primaries.

In an interview with NBC’s “Meet the Press,” the Arizona Republican and frequent Trump critic added that, if he did run for president, it would likely be only as a Republican.


Moreover, Flake, who is retiring from the Senate this year, said he hopes Trump draws a primary challenge.

“It's not in my plans. But I have not ruled anything out," Flake said. "I do hope that somebody runs on the Republican side other than the president, if nothing else, simply to remind Republicans what conservatism is. And what Republicans have traditionally stood for."

Flake added that Republicans in Congress need “to push back harder than we have” to rebuke Trump, citing concerns he could fire Robert Mueller, the special counsel investigating Russian meddling in the 2016 presidential election, or Deputy Attorney General Rod Rosenstein, who appointed Mueller.

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"I can tell you behind the scenes, there is a lot of alarm. There is concern that the president is laying the groundwork to move on Bob Mueller or Rosenstein. And if that were to happen, obviously, that would cause a constitutional crisis," Flake said.

"I've been concerned that we haven't spoken up loudly enough. And told the president, 'You simply can't go there,'" Flake said. "And he's obviously probing the edges as much as he can."

Pressed by anchor Chuck Todd on why Republicans haven’t been more critical of Trump, Flake — who faced a primary from a pro-Trump candidate before deciding not to seek another term — pointed to the difficulty many anti-Trump Republicans would have at the polls. And he said he hoped “many of my colleagues will find a voice” after primary season.

"This is the president's party. And if you're running in a primary right now, and you stand up to the president, or stand up in some cases for empirical truth, then you have trouble in primaries," he said.