Jeff Flake has regrets. Boy, does he ever.

Over his 16 years in Congress, the U.S. senator from Arizona has watched firsthand as his Grand Old Party first abandoned its aspirations as a party of ideals and principle and then devolved into a personality cult dedicated to the worship of a reality-TV star, a man who has no interest or ability in governance and whose personal life contradicts everything the party once claimed to champion.

A party that took pride in itself as a bulwark against vulgarity has embraced one of the most vulgar men in American public life as its hero. A party that used to proclaim itself more sober-minded and rational than its allegedly emotion-driven rival has now abandoned rationality altogether, indulging itself in "the sugar high of populism", as Flake puts it.

Yes, that approach has brought them political power, at least temporarily. But as we've seen, it has also stripped them of a real purpose toward which that political power can be put. To borrow the famous question from the Book of Matthew, "what does it profit a man to gain the whole world, yet forfeit his soul?" Or as Flake frames it in his new book, “Conscience of a Conservative,” "If ultimately our principles were so malleable as to no longer be principles, then what was the point of political victories in the first place?"

"We cannot claim to place the highest premium on character, then abruptly suspend the importance of character in the most vital civic decision that we make," Flake writes. "When we excuse on our side what we attack on the other, then we are hypocrites. If we do that as a practice, then we are corrupt. If we continually accept this conduct as elected officials, then perhaps we shouldn't be elected officials."

As that passage suggests, Flake blames himself and other conservatives for letting all this happen, for sacrificing integrity, principle and even a foundation in reality in exchange for short-term electoral success, and for "turning our democracy over to carnival barkers and reality TV."

"We pretended that the emperor wasn’t naked,” Flake writes of Donald Trump and the 2016 elections. “Even worse: We checked our critical faculties at the door and pretended that the emperor was making sense.”

Not surprisingly with talk like that, Flake is already drawing primary opposition next year from opponents who accuse him of political treason. Also not surprising, those opponents are getting a lot of encouragement from the Trump administration. Trump himself talks of spending $10 million out of his own pocket to defeat Flake, although as a long line of hoodwinked charities will attest, such talk rarely results in Trump writing a check.

Most damning of all, Flake is being accused of not being a true conservative, of being the dreaded "Republican In Name Only," a label that few survive these days.

From my own outsider point of view, Flake certainly appears to be conservative, because on a policy basis I agree with him on almost nothing. His voting record on issues from taxes to abortion to the role of government have been thoroughly right wing throughout his career.  Then again, as an outsider, I don't get to make that kind of decision. I don't get to define terms such as conservative and Republican, nor do I get to decide who gets included and excluded from them.

However, if a person cannot oppose and criticize the likes of Trump and still be considered conservative, then that's important for the rest of us to know. Among other things, it means that Trump's takeover of the GOP and the conservative movement is more complete than I might have realized. It means that its conversion to a personality cult may not be reversible anytime soon, at least not without fatal damage to the party itself.

As Flake also acknowledges, the problem runs deeper than Trump, who in many ways is a symptom rather than the cause of the GOP's ills. In medical terms, Trumpism is an opportunistic infection, attacking an already weakened host. The Arizona senator traces the disease back to the rise of Newt Gingrich and others, and to an increasing reluctance by party leaders to tell voters the truth or even to acknowledge that verifiable truth exists and that policy should be based on it. Flake condemns not just the birther movement, for example, but more importantly the party's decision to milk it and leverage it for political gain rather than confront it as a dangerous lie.

"When particular ugly conspiracy theories go out, or simply fake news, stuff that is just demonstrably false, we ought to stand up and say, ‘Hey, that’s just not right',” Flake says. And that extends to policy questions as well.

"It’s first and foremost the duty of conservatives to tell the truth to the constituency, and it’s easy to point to a shuttered factory and say, 'Hey, if we’d just negotiated better trade deals, then those jobs would be there.' When really it’s automation and productivity gains," Flake says.

In a sign of how distorted things have gotten, Flake undermines his standing as a conservative and Republican just by making that argument in favor of truth and fact-based policy-making. It marks him as someone outside the tribal consensus, and that's a dangerous place to make a stand in this environment.