Here's what you need to know about the Breitbart News chairman who just became Donald Trump's new campaign CEO. (Jenny Starrs/The Washington Post)

At the lowest point of Donald Trump’s quest for the presidency, the Republican nominee might have brought in a political handyman to sand his edges. Instead, he put his campaign in the hands of a true believer who promises to amplify the GOP nominee’s nationalist message and reinforce his populist impulses.

“Steve Bannon is a fighter’s fighter. He is somebody who wants to be the first boots on the beach. In the military, it’s called the tip of the spear,” said David Bossie, a conservative activist. It was Bossie who five years ago introduced Trump to Bannon, the top executive of the new media clarion of the establishment-­loathing right, Breitbart News.

Breitbart has since become a champion of Trump’s candidacy — in large part because Stephen K. Bannon himself believes it represents a cause much bigger than a political campaign. Bannon sees Trumpism as part of a global movement that will continue, no matter who is sitting in the Oval Office next January, those close to him say.

Last September, when hardly anyone else on this side of the Atlantic was taking the prospect of a British exit from the European Union seriously, Bannon invited influential Republican leaders to a dinner for Nigel Farage, the head of the UK Independence Party, at the Capitol Hill townhouse known as the “Breitbart Embassy.”

Bossie and others hailed Bannon’s pick as a sign that Trump, whose campaign has wobbled since the GOP convention, will return to the messages that won him the Republican nomination.

The Fix's Chris Cillizza explains why Donald Trump demoted campaign chief Paul Manafort and added two new top advisers – Breitbart News chief Stephen Bannon and pollster Kellyanne Conway. (Peter Stevenson/The Washington Post)

“It’s been frustrating that the campaign is not as vibrant and agile as we thought it could be at this stage,” Bossie said. “Steve is all action, action, action.”

Democrats saw a darker, more divisive turn in the selection of Bannon to hold the new title of chief executive.

Robby Mook, campaign manager for Democratic nominee Hillary Clinton, told reporters on Wednesday: “We absolutely expect, with this change, for Donald Trump and the campaign as a whole to double down on more conspiracy theories, more hateful rhetoric, more wild accusations.”

Mook also called Breitbart News a “divisive, at times racist, anti-Muslim conspiracy news site,” citing a report earlier this year by the Southern Poverty Law Center, a legal advocacy organization.

One headline last October dubbed Bannon “the most dangerous political operative in America.”

In that Bloomberg News article, Joshua Green reported that Andrew Breitbart, the late founder of the site, had “described Bannon, with sincere admiration, as the Leni Riefenstahl of the Tea Party movement,” a reference to the infamous and glamorous maker of Third Reich propaganda films.

Moviemaking has been one of the many chapters of Bannon’s career, which had previously included four years aboard a Navy destroyer, a post-MBA stint with Goldman Sachs, and founding an investment firm specializing in media.

In one particularly felicitous deal, Bannon’s fee included an early stake in “Seinfeld,” the residuals of which alone would turn out to be enough to make him wealthy.

Along the way, he developed a worldview remarkably in tune with what is now regarded as Trumpism: suspicious of free trade and liberal immigration policies, wary of military adventurism, and contemptuous of the old order.

Bannon grew up in a working-class Democratic family in Norfolk, Va. He has attributed his disillusionment with the Democrats to his years in the Navy under Jimmy Carter as commander in chief, and said his experience running businesses in Asia while George W. Bush was president convinced him that establishment Republicans were no better.

Bannon met Andrew Breitbart at a Beverly Hills screening of a 2004 Bannon-produced documentary on Ronald Reagan.

“We screened the film at a festival in Beverly Hills,” Bannon told Bloomberg’s Green, “and out of the crowd comes this, like, bear who’s squeezing me like my head’s going to blow up and saying how we’ve gotta take back the culture.”

At the time, Breitbart was trying to get his own website going, after having been an editor for the conservative aggregator Matt Drudge and a researcher for Arianna Huffington’s left-leaning Huffington Post. Bannon signed on to Breitbart’s new venture.

After Breitbart’s death from heart failure in 2012, Bannon vowed to carry on his vision by building a global operation of “real hell fighters.”

His operation has a more wonkish side as well, in the form of the nonprofit Government Ac­count­ability Institute, which pro­duced the best-selling book “Clinton Cash: The Untold Story of How and Why Foreign Govern­ments and Business Helped Make Bill and Hillary Rich.”

Trump was not the first po­tential president to catch Bannon’s eye.

In 2011, Bannon released a two-hour documentary about Sarah Palin called “The Undefeated,” attempting to reshape the way that voters and the media viewed the former candidate for vice president.

“The reason she draws this kind of fire is that she is an existential threat to the establishment,” Bannon told Fox News’s Sean Hannity during the film’s promotional tour. “The vested interests in our country are scared to death of her.”

While Palin dithered about whether to run for president, the documentary flopped, grossing $116,381. But Bannon remained convinced that the GOP was ripe for a populist takeover. That, say former employees of the site, was what set up the site’s aggressive coverage of illegal immigration, and what turned into the most pro-Trump news source.

In March 2014, after BuzzFeed’s McKay Coppins ran an unflattering report on what happened after traveling with Trump’s “fake” presidential campaign, Breitbart published a series of stories in which Trump allies attacked the reporter. “This nervous geek isn’t fit to tie the Donald’s wing tips,” Palin said, defending Trump against Coppins.

When Trump became a candidate for president, the relationship deepened, and the billionaire frequently made himself available to break news on his race.

He went to Breitbart to mock Jeb Bush for speaking Spanish and to attack Republicans for “folding” on trade. In a typical interview, conducted in November, Bannon joked that he himself had gone to “the poet’s version of business school — Harvard,” and he helped Trump dump criticism on the Republicans’ “consultant class.”

Former employees of Breitbart describe a work environment that mirrors the Trump campaign. Reporters who couldn’t break or match news were chewed out with profanities; reporters on his good side were drawn into a hypercompetitive battle to own the news.

All were encouraged to sign contracts with strict nondisclosure agreements. Several described Bannon pushing reluctant reporters onto stories by telling them: “I didn’t get where I am by being a Boy Scout.”

In March 2016, after Trump won Florida and held a news conference, Breitbart reporter Michelle Fields tried to ask Trump’s then-campaign manager Corey Lewandowski a question and was pushed aside.

Chat logs later obtained by BuzzFeed revealed that Breitbart leadership wanted Fields to lay off the story and for members of the team to avoid tweeting about it. Fields quit, followed by several Breitbart staffers, including longtime editor-at-large Ben Shapiro.

“He’ll tell Trump he’s doing a fantastic job even if he isn’t,” Shapiro wrote Wednesday on his new site, The Daily Wire. “That’s how Bannon Svengalis political figures and investors — by investing them in his personal genius, then hollowing them out from the inside. There’s a reason Sarah Palin went from legitimate political figure to parody artist to Trump endorser, with Steve Bannon standing alongside her every step of the way.”

“A lot of the people that you like and respect have targets on their backs as a result of Bannon’s ascent to the top,” wrote Ben Howe, an editor at the conservative blog Red State who had spoken out against Trump. “You have no idea how dangerous this man is. It is going to be score settling time for him if Trump wins. “

“If Donald Trump won the election, and Steve Bannon were his chief of staff, I would have legitimate fears about the use of government power to come after political enemies,” Shapiro said. “I don’t think Steve Bannon has principles.”

But a current employee of Breitbart, who had not been authorized to speak for the record, disputed that characterization of his boss: “What he does is he gets the best out of people.”

That, it would appear, is what Trump is hoping, as well.