Story highlights Flake: "The direction he's headed right now, just kinda drilling down on the base rather than trying to expand the base -- I think he's inviting one."

Flake, who is up for re-election in 2018, has been a frequent critic of Trump.

(CNN) Republican Sen. Jeff Flake said Wednesday that President Donald Trump is inviting a primary challenge in 2020 with his style of governing.

Flake, who is up for re-election in 2018, has been a frequent critic of Trump. The President, without naming him, called Flake weak at a rally in the senator's home state of Arizona on Tuesday. Trump has also tweeted positively about Flake's primary opponent Dr. Kelli Ward and has met privately with two other potential primary challengers/

Asked on Georgia Public Broadcasting's "Political Rewind" Wednesday about whether Trump could face a primary challenge of his own in 2020, Flake said he didn't know.

"I think that certainly depends on him," Flake said. "I think he could govern in a way that he wouldn't. But, I think that the way that -- the direction he's headed right now, just kinda drilling down on the base rather than trying to expand the base -- I think he's inviting one."

In a tweet also on Wednesday, Trump wrote that Arizonians in Phoenix were not a fan of Flake: "Phoenix crowd last night was amazing - a packed house. I love the Great State of Arizona. Not a fan of Jeff Flake, weak on crime & border!"

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