Sen. Jeff Flake believes conservatives helped create the conditions for the rise of President Trump and are emboldening "instability" in the White House by not speaking out more.
"We created him, and now we're rationalizing him. When will it stop?" Flake wrote in his new book, "Conscience of a Conservative," an excerpt of which Politico published on Monday.
Flake, R-Ariz., a fiscal conservative with an independent streak who is seeking re-election next year, said conservatives "ensured the rise" of Trump by contributing to increasing polarization in politics.
He criticized conservatives who "mocked Barack Obama's failure to deliver on his pledge to change the tone in Washington even as we worked to assist with that failure."
He questioned Senate Majority Leader Mitch McConnell's promise to make Obama a one-term president, rather than prioritizing a conservative policy agenda.
He blamed conservatives for playing a part in legitimizing false attacks against Obama questioning his U.S. citizenship.
And he said his party has not done enough to contest some of Trump's behavior, policies, and rhetoric.
"As the first branch of government (Article I), the Congress was designed expressly to assert itself at just such moments," Flake said. "It is what we talk about when we talk about 'checks and balances.' Too often, we observe the unfolding drama along with the rest of the country, passively, all but saying, 'Someone should do something!' without seeming to realize that that someone is us.
"And so, that unnerving silence in the face of an erratic executive branch is an abdication, and those in positions of leadership bear particular responsibility."
Flake's book, which he wrote in secret without telling his political advisers, is part of his re-election campaign.
Flake is facing pressure from the both sides of the aisle as he seeks to preserve his Senate seat in 2018.
Allies of Trump aim to punish Flake and may help draw a conservative primary opponent against him for his outspoken rejection of Trump, the New York Times and others have reported. Flake never endorsed Trump in the campaign and called for him to withdraw from the race after the release of the "Access Hollywood" tape.
He has continued to oppose Trump as president.
In his book, Flake wrote he is particularly concerned about Trump's "seeming affection for strongmen and authoritarians" such as Russian President Vladimir Putin, and his protectionist trade policies.
He also called on senators to preserve the filibuster, which Trump has repeatedly said he would like to see eliminated.