David Brock is an incorrigible liar.

He is possibly the least honest man ever to succeed in American journalism.

The misdemeanors of fabulists such as Jayson Blair and Stephen Glass had little significance beyond embarrassing some editors, but Brock helped wreck a presidency with his Troopergate reporting.

Brock has apologized for that and for trashing Anita Hill and threatening to smear the source of a particularly damning anecdote about Clarence Thomas.

Yet this admitted liar has somehow resuscitated his career, as an arbiter of honest journalism no less.

The thing is: Brock never changed. He’s still a hit man, just for the other team. He was on MSNBC just the other night calling Fox News chairman Roger Ailes a racist, based on a 45-year-old quote he had ripped from context (which we’ll revisit).

Ailes had used “the N-word prepping Richard Nixon for a public appearance,” Brock charged inaccurately, before rushing on to list more random and spurious evidence against him.

The vicious and unsupported personal attack was striking coming from Brock. Here is a man whose acceptance in the mainstream media is due entirely to his story of repentance and conversion, yet his sins are so odious that one has to think not that he’s a backslider, but that he never saw the light at all.

From 1997 to 2002, Brock wrote several drafts of his conversion story. From “Confessions of a Right-Wing Hit Man,” published in Esquire, to the final, book-length version, “Blinded by the Right: The Conscience of an Ex-Conservative,” Brock developed a narrative aimed at ingratiating himself with the left.

It worked. In The New Yorker, Hendrik Hertzberg vouched for the conversion from hit man to respectable Democrat.

“What drove Brock was the wrongness of what he did, not of what he thought,” Hertzberg wrote. It’s “the story of a change of heart, not of mind.”

Hertzberg, like many, didn’t look too closely at the details of the story. In “Confessions,” Brock was still insisting he’d told the truth. In “Blinded,” he elides lie after lie, lies the reader wouldn’t recognize without close knowledge of the Thomas confirmation affair.

But when Brock’s telling the story, it works. In fact, he raises millions telling it to donors.

“Seeing the things he couldn’t deal with over there on the conservative side and then being abused because of his sexual ­preference — his whole story was just compelling to me,” said billionaire Peter Lewis, one of his biggest donors.

Now Brock shows up on talk shows and is quoted in newspapers criticizing journalists, as if he had any standing better than shamelessness to do so.

The whole basis of Brock’s respectability is his repentance for his underhanded tactics, yet he is every bit as devious, deceptive and malicious in his attacks on Fox News as he was 20 years ago.

So why does anyone think it’s OK to quote him or invite him on a TV show?

There’s one influential journalist who hasn’t been fooled, though.

Despite his ubiquity in national media and his embrace by star Democrats, Brock is not welcome in the pages of The New York Times. Since Jill Abramson took over as executive editor of the Times nearly two years ago, Brock has been quoted in the paper exactly once, and that was to talk about campaign fundraising, according to a search ofLexis-Nexis.

His only other mention in the paper in that time was in a review of his book and a related letter to the editor. His organization, Media Matters for America, has been cited in just a handful of stories.

Journalists elsewhere may have gradually and unthinkingly accepted the notion of Brock’s respectability, but Abramson knows his duplicity too well.

Abramson and her then-colleague at The Wall Street Journal, Jane Mayer, wrote a meticulously researched book, “Strange Justice,” in 1994, on the Thomas/Hill affair, a book intended to clear up many of the lies and distortions that Brock created with his own book and sensational articles in The American Spectator.

“I never saw his credibility as being strong, because when his book came out I saw that factually it was shot full of holes right from the start,” Abramson told Howard Kurtz in 2001. “I could see the flaws in the book, but it was presented as, you know, a very carefully researched book.”

When Abramson and Mayer’s book was published, Brock falsely accused them of trying to pull “one of the most outrageous journalistic hoaxes in recent memory.” In the January 1995 American Spectator, he wrote a 20,000-word defense of his reporting consisting of lie piled on pathetic lie – lies about what sources had told him and easily refutable lies about what Abramson’s book said.

It was while working on that piece, Brock wrote later, that he realized, “I was no better than the Arkansas Project brigade after all. The strange lies were mine. All the attacks, the hateful rhetoric, the dark alliances and strange conspiracies, an eye for an eye, nuts and sluts, defending Pinochet, throwing grenades, carpet-bombing the White House, Bob Bork, Bob Tyrrell, Bob Dornan, Bob Bartley, Bob Barr — it all led right here: I lost my soul.”

Yet he published the lying response anyway. Worse, his “confession” in “Blinded by the Right” skips right over his endless distortions and lies. Brock doesn’t own up to the rampant dishonesty, instead comparing his efforts to the work of a defense lawyer:

“I knew the ins and outs of the case better than anyone, and I knew how to twist and turn them to our advantage. I had done this previously, in my book, in the service of a sincerely held belief. Now, I wasn’t sure why I was doing it. I was just doing it…Donning my defense lawyer hat, I dissected the Mayer and Abramson excerpt, methodically turning back each new damaging allegation they raised and patching up the sizable holes they had shot in Thomas’s defense.”

“Turning back” is one way to put it. Another is “lying nonstop about,” but it’s hard to get anyone’s sympathy that way.

The one lie he admits to there “was small,” Hertzberg wrote, “but it was where Brock now understands that he touched bottom. It took him several more years to feel his way up through the dark, noxious mass he had done so much to create.”

Not everyone is willing to credit Brock’s time-lapse Road-to-Damascus story, given his continuing dishonesty in “Blinded by the Right.”

“I would say without any hesitation that he is incapable of recognizing the truth, let alone of telling it,” Christopher Hitchens wrote after reading Brock’s memoir. “The whole book is an exercise in self-love, disguised as an exercise in self-abnegation. How could he, asks the author of himself, have possibly gone on so long in telling lies, smearing reputations and inventing facts? The obvious answer — that he adored the easy money and the cheap fame that this brought him — was more than enough to still his doubts for several years. However, his publisher seems to have required a more high-toned explanation before furnishing him with a fresh tranche of money and renown. And Brock’s new story — that he was taken in by a vast right-wing conspiracy — is just as much of a lie as his earlier ones.”

Brock’s conversion story includes a date, and “the date makes it easy to demonstrate that Brock is a phony,” Hitchens writes, before doing just that.

An essential aspect of repentance is admitting own’s one responsibility, yet Brock shifts responsibility to others, from the title of his book to sentences like this: “I was miserable. Yet this was how I made my living and it was who I had become. The conservatives had bought my brain.”

“Who is such a sap as to take the word of such a person,” Hitchens asks, before concluding that the “defamation game is still all that this creep knows.”

Timothy Noah of Slate wrote that the “further one gets into Brock’s book, the more one starts to suspect that Brock wasn’t a liar for any larger cause, but simply…a liar.”

“Blinded by the Right offers plenty of evidence that for Brock, lying has been a lifelong habit,” Noah wrote. “During his freshman year at Berkeley, when Brock was still a Naderite liberal, he lied to a man named Andrew, who would become his lover, about the fact that he was adopted. Andrew didn’t learn the truth until after he and Brock had lived together many years. While campaigning to be editor in chief of the Daily Cal at Berkeley, Brock was ‘caught in an embarrassing lie’ about an editor he didn’t like. He told the Daily Cal’s outgoing editor in chief that the university’s vice chancellor had phoned to complain about a story that the enemy editor had presumably mangled. It wasn’t true, and Brock got caught. By this time Brock had drifted right, but he offers no evidence that this particular conflict had any ideological content. Years later, Brock leaked his American Spectator piece about Troopergate to CNN, contrary to orders from his editors, who were enforcing an embargo on it. ‘When confronted, I came up with a clearly implausible lie,’ Brock confesses.”

Then Noah goes and points out several lies Brock tells in the book.

Yet all the lies and specific dishonesty gets obscured by the soft-focus story his friends tell, one of apology and redemption and seriousness of purpose.

As late as 2011, a fawning writer in New York magazine could write that Brock “speaks deliberately, seldom raising his voice or even moving his hands, as if he fears one intemperate or ill-chosen word could undo all of the hard work that has gone into his re­invention…And whereas he used to think of himself as a conservative action hero — ‘I kill liberals for a living,’ he once declared — he now reaches for a more mundane analogy to describe his role on the left. ‘I’m kind of a builder of institutions,’ he says. ‘I think I’ve got some ability to look at what’s out here, look at a playing field, and identify gaps and niches.'”

Former Senate Majority Leader Tom Daschle vouches for the description, telling the writer, “I don’t know if anybody has a better understanding, in the broader context, of how institutionally we have to go about building a more politically potent force for the progressive movement than David.”

At the same time media allies were trying to portray him as a mild, respectable builder of stuff, the real Brock was telling others of his plans to wage “guerilla warfare and sabotage” against Fox News.

He’s done just that. On the rare occasions The New York Times deigns to mention Media Matters, it no longer identifies the organization as a “nonprofit watchdog” or a “media monitoring group.” Now it’s simply an “anti-Fox group.”

Last week, Brock was on Al Sharpton’s MSNBC show, throwing the same kind of low blows that made him infamous. His dirtiest claim was that “back in 1968, you had Roger Ailes, who’s now the Fox News chief, using the N-word prepping Richard Nixon for a public appearance. This was part of the Southern Strategy at the time, to attract Democrats into the Republican Party by stoking racial hate and prejudice.”

A lot more recently than 1968, Brock was using now-verboten terms like “fag hag,” but that doesn’t mean much of anything without the context, does it?

The context Brock deliberately omits is found in Joe McGinniss’ famous book, “The Selling of the President.” Ailes was speaking not for himself, but imagining what a “Wallaceite cab driver” might say if he were put on TV to ask Nixon a question.

Ailes’ role in the 1968 campaign was to organize a series of 10 televised town hall meetings, all live, all unstaged. Unlike the play-it-safe consultants of today, Ailes followed his showman’s instinct to make each hour-long broadcast as riveting as possible.

McGinniss writes that “there was nothing (Ailes) could do about what Nixon would say or would not say, but he did not want anyone turning off before the hour was over.”

Ailes thought Nixon was at his best when challenged, so he avoided softball questioners.

“I’m convinced we need legitimately tough panels to make Nixon give his best,” Ailes told the author. “In Ohio, where we just came from, we had a strong panel and it was by far the best show of the three.”

“The problem with the panels is that we need variety… Nixon gets bored with the same kind of people. We’ve got to screw around with this one a little bit.”

He also tried to make the panels reflect demographics. As McGinniss put it: “Fourteen percent of the population applied to a six- or seven-member panel equaled one.”George Wallace, coincidentally or not, got 14 percent of the popular vote that year.

One of Ailes’ ideas, according to McGinniss, was to find “a good, mean, Wallaceite cab-driver. Wouldn’t that be great? Some guy to sit there and say, ‘Awright, Mac, what about these niggers?'”

Nixon would have recoiled from any question of that sort, of course, but nobody would have been changing the channel.

While the Nixon campaign did try to send coded messages to Southern voters to dampen enthusiasm for Wallace, the messages were much more sedate. The campaign would run a country song about taking back the nation during a wrestling broadcast, or Nixon would express disapproval of civil disobedience “as long as change could be brought about within the system,” according to McGinniss.

Ailes acted on his idea and went to the cab stand outside his hotel.

“The third driver Roger Ailes talked to said he was not really for Wallace, but he wasn’t against him either,” McGinniss wrote.

Frank Kornsey was his name, and Ailes invited him on the show.

The question Kornsey ended up asking, at least the question recorded by history, was about the USS Pueblo, a spy ship captured by North Korea in1968.

Brock leaves all that out, of course, as it would dull the edge of his blade.

Two years ago, a reporter asked Brock what he stood for other than tearing down the right. After a long pause, this was his answer: “A lot of what I think about is tolerance in the debate and trying to tamp down on the toxicity of it all. So, if you’re asking me why am I a progressive, those are kind of the ways that I think about it. But I also think of it frequently in opposition to what the right is doing.”

Brock had a decade to come up with something about progressivism that he supports, and he still hasn’t managed. Instead, the most promiscuous slanderer of his generation says that he is an agent of tolerance.

You have to ask: Is Brock a little bit nutty? Or just a little bit slutty?

Jon Cassidy is a reporter for the Franklin Center. This article originally appeared at the Franklin Center’s Watchdog.Org.