Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeRepublican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style Bush endorsing Biden? Don't hold your breath MORE (R-Ariz.) on Tuesday defended his risky political move to criticize President Trump's administration in his new book, saying there are some things that "are more important than a political career."

"Yeah, it would have been probably politically smarter to wait until you're safely reelected to write a book like this, but then it wouldn't mean as much," the Republican senator told host Jake Tapper on CNN's "The Lead."

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"If you don't have anything to risk politically, it doesn't mean as much. I felt that it was important enough to stand up and write this. So I've done it," said the lawmaker, who is up for reelection in 2018.

His remarks come in response to reports that say the White House is considering backing primary challengers during the midterm election next year in an attempt to thwart Flake's reelection chances.

Flake, who has been making the news network rounds to promote his latest book "Conscience of a Conservative," has been publicly criticizing the president and calling on his Republican colleagues to also take a stand.

Flake, who recently said GOP lawmakers who don’t stand up to Trump are complicit with his actions, wrote an op-ed for Politico Magazine in which he called on his Republican colleagues to stand up to Trump when they notice his rhetoric and policies have gone astray.

He added that many Republicans have been in denial during the first months of the Trump presidency.

“To carry on in the spring of 2017 as if what was happening was anything approaching normalcy required a determined suspension of critical faculties. And tremendous powers of denial,” Flake wrote in the op-ed.