President Donald Trump on Thursday took aim at a potential 2020 GOP primary foe, using retiring Sen. Jeff Flake’s last name as a rhetorical bludgeon.

The retiring Arizona senator has not ruled out a presidential bid and — unlike others in his party — has been a vocal critic of Trump.

“How could Jeff Flake, who is setting record low polling numbers in Arizona and was therefore humiliatingly forced out of his own Senate seat without even a fight (and who doesn’t have a clue), think about running for office, even a lower one, again?” Trump tweeted.

“Let’s face it, he’s a Flake!” Trump wrote, appearing to suggest the name somehow makes the Republican member weak politically.

How could Jeff Flake, who is setting record low polling numbers in Arizona and was therefore humiliatingly forced out of his own Senate seat without even a fight (and who doesn’t have a clue), think about running for office, even a lower one, again? Let’s face it, he’s a Flake!

— Donald J. Trump (@realDonaldTrump) June 7, 2018

Late last month, Flake was noncommittal on a presidential bid and said he hopes someone in the party will challenge Trump.

“It’s not in my plans. But I have not ruled anything out,” Flake said on NBC’s “Meet The Press” program May 27.

“I do hope that somebody runs on the Republican side other than the president, if nothing else, simply to remind Republicans what conservatism is,” he said. “And what Republicans have traditionally stood for.”

Wrestling the GOP nomination from the president would likely be tough. Trump regularly garners approval ratings among Republican voters in the high 70s and low 80s.