The book pulls no punches.

It sharply condemns conservatism for its role in a “culture of vicious dehumanization,” not to mention its sins of incoherence, rejection of empirical fact and plain hypocrisy. Writing of the rush by the conservative party, i.e., the Republican Party, to embrace the regrettable Donald Trump during the last election, the author is blunt and unsparing. “Never has a party so quickly or easily abandoned its core principles …”

No, these are not new complaints; they have been made repeatedly in recent years. But what makes this particular bill of charges against conservatism and the Republican Party noteworthy is not the substance, but the source.

Meaning, a self-described “proud conservative and a lifelong Republican” – U.S. Sen. Jeff Flake of Arizona. Flake’s new book, “Conscience of a Conservative” – the title is an ode to Barry Goldwater’s 1960 tome of the same name – takes conservatism and the Republican Party to task in no uncertain terms. It’s being called an act of moral courage. It might even be one.

At the very least, the book is timely, particularly in its lamentation of the hatefulness – the word is not too strong – of the nation’s political divide. Flake captures this starkly in one painful anecdote:

January 2012, President Obama’s State of the Union address. Flake is sitting next to a friend, Democratic U.S. Rep. Gabrielle Giffords, who is still recovering after being shot in the head the year before. “During President Obama’s applause lines, Gabby wanted to stand up but was unable to do so on her own, so I helped her. That often left me standing, a lone Republican among cheering Democrats.”

He stood, he writes, not to support the president, but to help “a cherished and brave colleague.” Which should have been patently obvious to anyone with eyes and a functioning conscience, but it apparently made little difference to those who sent him “furious text messages and emails” during and after the speech, taking him to task for this act of political apostasy.

As noted, Flake’s “Conscience” is being widely lauded. The Washington Post called it “brave.” USA Today dubbed it “courageous.” Columnist Michael Gerson said it was “the single largest act of political bravery of the Trump era.”

You’ll get no argument here. But you will find an observation: This courage would be more impressive had it shown itself sooner. The Republican Party, after all, didn’t lose its mind when Trump came to town. Rather, it was the loss of its mind that made Trump possible. And that loss predates his presidency by a good two decades.

How much of the dysfunction of those years – the baseless 24/7 investigations, the birther idiocy, the Islamophobia, the death panels, the obstructionism – might have been ameliorated by a little in-the-moment conservative courage? Republicans are not asked to abandon their low-taxes, small-government orthodoxy. No ideology, after all, has a monopoly on good ideas.

But this is not about ideology. Rather, it’s about the Republican Party’s en masse retreat from reason, responsibility, statesmanship and simple decency.

This retreat has been objectively obvious for years, but the list of Republicans willing to stand up and concede the objectively obvious has been pathetically small. Now Flake adds his name, making it … slightly less small.

Brave? OK. But that bravery is irrelevant until and unless his conservative conscience touches someone else’s. His party, his people, need to acknowledge their dysfunction, need to own it – and fix it.

Otherwise, he’s still standing alone while the wrong people applaud.

Leonard Pitts Jr., winner of the 2004 Pulitzer Prize for commentary, is a columnist for The Miami Herald. He can be contacted at:

lpitts@miamiherald.com