For the past few decades, Dinesh D'Souza has been on a downward slide from proto-intellectual to internet troll. He has finally reached the Godwin's law stage of development with his new book, "The Big Lie: Exposing the Nazi Roots of the American Left" (which presumably had the working title "I Know You Are But What Am I?").

The decline of D'Souza, author of books like "The Roots of Obama's Rage" and "The Enemy at Home: The Cultural Left and Its Responsibility for 9/11," would not be particularly notable, except that it mirrors the unmaking of the Republican Party more broadly. This is not a coincidence: D'Souza was a conman in search of a mark, and he found it in the Republican base. That makes his career arc useful for people curious about the devolution of the GOP into a party committed to nothing other than tribal politics.

For a book about secret Nazis, "The Big Lie" is surprisingly dull. Jonah Goldberg covered this tenuous (and tedious) argumentum ad Hitlerum ground better a decade ago in "Liberal Fascism," where we learned that Hitler was a vegetarian so we should be wary of laws mandating calorie-counts in restaurants, or something. "The Big Lies" adds to that argument some decorative D'Souzian grotesquerie – most notably when he compares Trayvon Martin, a young kid murdered while walking home, to Horst Wessel, a Stormtrooper who became part of Nazi lore – but that's just the trollish icing on the stale cake of the liberal fascism line.

"The Big Lie" thus adds little to the no-you're-the-fascist genre on the right. But it's illuminating when placed in the context of D'Souza's own work. As someone who's inflicted herself with a great deal of D'Souza's weaponized pseudo-history, I had my lightbulb moment about a third of the way through the book, when he began making direct comparisons between the Holocaust and Indian removal in order to show that the Nazis took their inspiration from Democrats.

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D'Souza writes mournfully of the genocide of American Indians in the early 19th century. Which I found curious, because in an earlier book in which he denounced the "shame narrative" of American history, D'Souza flatly stated that "there was no genocide" of American Indians, that this was just another Big Lie by the left to make Americans ashamed of their country. But three years later, D'Souza now sees an American history not only littered with unspeakable crimes, but one that is responsible for inspiring the Nazis' catalogue of horrors.

Sorry, did I say American history? I meant Democratic history. D'Souza has since concluded that "neither 'the West' nor 'America' is guilty of genocide; rather, Andrew Jackson and the Democratic Party are." And that's a big deal, because it is predicated on the belief that there is no American history as a unitary story, one in which the actors of the past, for good and ill, have contributed as Americans to the national history.

D'Souza thus tries out a new approach, one that builds on "the secret history of the Democratic Party" that he trotted out in "Hillary's America" and that reflects the stark polarization and tribalism of contemporary GOP politics. Slavery is not a national sin, but a Democratic one. Same with segregation, same with Indian removal, same with eugenics. (That Donald Trump lionizes Andrew Jackson gets only a shrug: "Trump, like Reagan, is a former Democrat.")

That type of tribalism runs deep in "The Big Lie," as D'Souza, a one-time conservative ideologue, outs himself as a pure partisan. Case in point: His discussion of the Supreme Court and the need to ensure it is "made up of people on our team." When D'Souza says "our team," he's not talking about conservatives: "During the Gorsuch hearings, Republicans kept stressing that [Neil] Gorsuch is a good constitutionalist. I'm good with that. But the question I wanted to have answered was a different one – is Gorsuch a good Republican?"

That's a pretty shocking declaration, even for a book that elsewhere declares that "Nazi DNA was in the Democratic Party from the very beginning." That's because at the end of the day, the Nazi stuff is just a gimmick to sell books. The stark tribalism? That's a governing philosophy that has taken over the GOP.

In the end, "The Big Lie" is a book about the Republican, not the Democratic, Party. That becomes clear in the final chapter on the "denazification" of the American left, in which D'Souza presents his "anti-fascist agenda." As it turns out, the best way to denazify America is to enact boilerplate Republican policies. Pass a simplified tax code to thwart the Nazi left! Repeal Dodd-Frank to conquer creeping fascism! This is dumb and deeply cynical, but D'Souza doesn't really care. He has your $20.