(Photo by Jabin Botsford/The Washington Post)

Bloomberg reporter Joshua Green’s much-anticipated new book about Steve Bannon and the rise of Trump is out today, sparking click-worthy headlines highlighting some of the White House strategist’s most profane pronouncements on politics, the media, and even Republican leaders like House Speaker Paul Ryan.

According to Green, Bannon once derided Ryan as a “limp-d*** motherf***** who was born in a petri dish at the Heritage Foundation.”

But for Republicans, at least, the most crucial takeaway from Green’s deeply reported “Devil’s Bargain: Steve Bannon, Donald Trump, and the Storming of the Presidency should not be Bannon’s stunningly foul mouth or his disdain for the institutional pillars of the conservative movement. In these pages Republicans will find something far more existentially dangerous: An account of how Bannon’s burn-it-all-down mentality is already in the process of destroying their party.

In many ways, Green’s book strips away the mystery surrounding Bannon, who is often portrayed in the media as a shadowy Svengali who is ultimately directing traffic in Trump’s chaotic West Wing. Bannon is frequently at the center of the palace intrigue stories that have gripped Washington since Trump took office, seeking to discern who is in and who is out of favor with the mercurial president — the “nationalist” contingent personified by Bannon, or the “globalist” group he reviles.

In this formulation, Treasury Secretary Steve Mnuchin and economic advisor Gary Cohn, both Wall Street veterans, are depicted as the “globalists,” part of an “elite” that sneers at Bannon’s supposedly populist base. Bannon’s (often white) nationalism is represented by Trump when he is railing on immigration or trade, or in speeches like the one he gave in Poland recently, questioning whether the “West” has the “will to survive.”

But as this book reveals, whatever happens in White House staffing, Bannon has already made his ruinous mark on the GOP — and that path of destruction could continue, regardless of White House staffing, and with or without Trump. Bannon, Green writes, “is a brilliant ideologue from the outer fringe of American politics” whose “unlikely path happened to intersect with Trump’s at precisely the right moment in history.” Bannon had cooked up the political movement; Trump became its standard-bearer.

In Trump, Bannon found a candidate who had been willing to transform himself, as early as 2013, in Green’s words, “into a full-blown hard-right populist, a political persona he now projected like cologne.”

It’s clear from Green’s reporting that Bannon played a key role in elevating Trump, who was the perfect, conspiracy-minded outsider who could step in as the anti-globalist, indeed anti-Republican GOP nominee. But in some ways Trump is a smaller player in a larger project whose aim is to radically reshape the Republican Party, a strategy Bannon set in motion before Trump’s viability as a political candidate came into view. And it’s evident that in reshaping the GOP by bolstering a candidate like Trump, Bannon has no compunction about destroying it.

Green’s book reveals new details as to how this project works. When Bannon took over the far-right news site Breitbart in 2012, Green writes, “the main discernible difference under his leadership was an amplification of the nativist populism,” and, notably, “an emboldened desire to attack ‘globalist’ Republicans.” Ryan, and before him, his predecessor John Boehner, were particular targets of Breitbart’s, and of Bannon’s acolyte Julia Hahn, who now works in the Trump White House, as a special assistant to the president.

As a reporter for Breitbart, Green writes, Hahn was one of Bannon’s “Valkyries,” one of “a group of beautiful young women” whom Bannon named “after the war goddesses of Norse mythology who decided soldiers’ fates in battle.” Ryan was Hahn’s “favorite target,” Green writes. She accused the House Speaker of “being a ‘third-world migration enthusiast’ and ‘double agent’ secretly pulling for Clinton.” On assignment in Ryan’s Wisconsin congressional district Hahn once used a photograph of a fence around Ryan’s home in an anti-Ryan story — a “Breitbart classic,” according to Green.

Bannon, Green writes, “loved it,” extolling how “s*** gets f***ed up” when Hahn “comes into your life.”

Although Bannon and his crew have not yet brought down Ryan, they did have success with former House Speaker John Boehner, cheerleading for “the growing mutiny among his hard-right flank” in 2015 — just as Trump’s presidential campaign was gaining steam. Faced with disparagement from Breitbart and Trump’s derision for the “very, very stupid people” leading the country, Boehner retired. This, Green suggests, only served to reinforce Trump’s campaign message of getting rid of the party leaders who weren’t serving the (Breitbart) base.

Once on board the Trump campaign in the summer of 2016, Bannon’s strategy was far more pernicious than expelling ideological enemies from the party. Last October, Green writes, Trump “channeled Bannon’s conspiratorial worldview” in a campaign ad that tied Hillary Clinton to “a global power structure that is responsible for the economic decisions that have robbed our working class, stripped our country of its wealth, and put that money into the pockets of a handful of large corporations and political entities.” After the Anti-Defamation League and others denounced the ad as peddling in anti-Semitic tropes, Green reports, Bannon told Trump that “darkness is good” and “don’t let up.”

There’s no reason to think that Trump and Bannon will let up on the darkness, and the Republican Party appears to be accommodating that. The GOP has stood by silently as Bannon boasted of having provided a platform for the alt-right, as Trump boasted of sexual assault, and Trump’s entire campaign of racism, xenophobia, and nativism.

But where is this all going to end up? The Republican Party, whose standard-bearer Ronald Reagan described America as a “shining city on the hill,” has now been enveloped by Steve Bannon’s darkness. While Bannon loses some battles, resulting in policy positions that seem to favor the “globalists” over the “nationalists,” his enduring mark on the GOP may not be on policy or legislation. Instead, he may end up making previously fringe ideas, particularly conspiracy theories about “globalists” or refugees or the Democratic Party, to name a few scapegoats, mainstream. Over time, that could shape the party more than Trump himself, with more lasting impact on how far the Republican Party is willing to diverge from the ideals of pluralistic democracy in order to minister to the illiberal, xenophobic base Bannon helped cultivate.