Before Steve Bannon could focus his full attention on Hillary Clinton, he had another unlikely nuisance to vanquish: Fox News.

The first Republican presidential debate in August 2015 will be remembered for Fox's Megyn Kelly's combative questioning of Donald Trump's distasteful comments about women. It was a full year before Bannon would even formally become a part of Trump's campaign.

And yet it was Bannon's response at that tenuous moment that brought the mighty conservative cable news juggernaut to its knees amid a highly charged GOP primary race.

Following that first debate, Bannon, the then-chairman of the virulently anti-establishment Breitbart News, decided to launch a concerted attack on Kelly and her credibility. Between the Thursday night when the debate took place and Sunday evening, Breitbart published 25 stories on Kelly and accused Fox of "trying to take out Donald Trump."

According to Joshua Green's new book, "Devil's Bargain: Steve Bannon, Donald Trump and The Storming of The Presidency," Fox News chief Roger Ailes was panicked.

"Steve, this isn't fair and it's killing us," Ailes called to tell Bannon. "You have to stop it."

Bannon's retort, in part: "F--- that."

Kelly didn't back down, continuing to mock and challenge Trump on her nightly program. But neither did Breitbart. Bannon himself composed a point-by-point case against Kelly titled, "The Arrogance of Power: Megyn Kelly's Good Journalism." Later, the debate fell into the gutter. Another Breitbart story read: "Flashback: Megyn Kelly Discusses Her Husband's Penis and Her Breasts on Howard Stern."

Trump was livid all the while too, taking his shots at Fox on his favorite medium, Twitter.

Out of options, Ailes, Green reports, dispatched his personal lawyer to Washington to plead with Bannon to stand down. But the attorney, Peter Johnson Jr., made a crucial mistake. He presented Bannon with a threat: If Bannon didn't stop his war on Fox's biggest star, he would never again appear on Fox News.

Bannon was incensed. It was the wrong way to approach the former naval officer who reveled in the darkest arts of conflict.

"She's pure evil," Bannon said of Kelly. "And she will turn on him one day. We're going full-bore. We're not going to stop. I'm going to unchain the dogs."

Besides, Bannon confessed to another associate, "The traffic is absolutely filthy!"

The conversation with Johnson was short and filled with venom.

To finish it, Bannon told him to go back to New York and "quote me to Roger."

"Go f--- yourself."

Every president has an essential strategist attached to him, an often cryptic figure who guides a politician through the political and policy quandaries of history. George W. Bush had Karl Rove. Barack Obama had David Axelrod. Green, a Bloomberg Businessweek correspondent, argues in his tome that Trump's political shepherd is unquestionably Bannon.

What's unique about Bannon is how much of his work he did on the periphery and how unlikely his path was to the helm of the final months of the Trump campaign and then ultimately to his current seat as chief strategist in the White House.

Bannon was initially introduced to Trump by David Bossie, a longtime conservative activist and chief agitator of the Clintons, to provide informal counsel on a presidential bid. But Bannon never thought much of Trump's chances at the outset.

Yet after the 2011 White House Correspondents Dinner, in which Trump was roasted by President Barack Obama and teeming from the humiliation, Bossie brought Bannon to Trump Tower for a meeting where they appeared to click on instinct.

Green lays out the striking similarities: "Like Trump, Bannon had cycled through multiple marriages, and was rich, brash, charismatic, volcanic, opinionated and never ruffled by doubt. He, too, was a businessman and a deal maker, and he had faced down moguls ranging from Ted Turner to Michael Ovitz. Fluent in the argot of Wall Street and Hollywood, Bannon specialized in media, having moved from financing television shows and films to making movies himself. He had plenty of experience maneuvering among the outsize egos of aggressive billionaires such as Trump and seemed to possess a sixth sense about how to connect with them."

Other Trump aides noticed the connection quickly. When Trump attended a conservative Freedom Summit event in South Carolina, Sam Nunberg, a former Trump aide, remembers the candidate-to-be cooing, "Where's my Steve? Where's my Steve?"

"It was clear the connection was genuine," said Roger Stone. "Because Steve is a slob and Trump hates slobs."

While Green's book is equipped with catchy quotes by Trumpworld's vast array of colorful players and enjoys early cooperation from Bannon, chapters go by where Bannon is left almost unmentioned and the reader is left to wonder his precise role in important Trump decisions. Much time is instead spent diving into the role of Bannon associates, like the author Peter Schweizer, who penned "Clinton Cash," and the strange and reclusive megadonor Robert Mercer who Bannon dubbed as "The Godfather."

The one area Bannon is directly tethered and devoted to from the outset is how to take out the Clintons. "My goal is that by Nov 8th, when you hear her name, you're gonna throw up," he said.

And it was his keen observation of how to learn and adjust from the past failed Clinton wars that proved crucial to the unforeseen winning 2016 strategy.

Bannon, Green writes, understood that Republicans blundered in defeating the Clintons in the 1990s because they overreached and overindulged loony theories to the point that they lost credibility with everyone but their own. Amassing unflattering facts about Clinton would be more powerful than beating the drum on far-reaching conspiracy-fueled storylines, Bannon asserted.

"Back then, they couldn't take down Bill because they didn't do that much real reporting, they couldn't get the mainstream guys interested, and they were always gunning for impeachment no matter what. People got anesthetized to outrage," Bannon is quoted telling Green.

That's why Schweizer's book became so important; it was an outlet to establish a series of facts, (along with some partisan assumptions) that targeted only the last decade of the Clinton Foundation and its web of questionable financial entanglements across the globe as Hillary Clinton served as the nation's chief diplomat.

Much of the information that Schweizer and Bannon dug up was placed first not in Breitbart, but The New York Times, which had millions of Democratic readers and was guaranteed to be picked up by the rest of the media, as the gold standard of journalism. Of course, then Breitbart and Drudge could use the Times' stamp of approval to carry the narrative and take it to more extreme anti-Clinton heights.

"We're aggregating, we'll pull stuff from the left. It's a rolling phenomenon. Huge traffic. Everybody's invested," Bannon said.

Green even found that Democrats noticed Bannon's more sophisticated approach to implementing the "vast right wing conspiracy" against the first female presidential nominee of a major party.

"They've adapted into a higher species," said Chris Lehane, a Clinton White House staffer.

Even with all that ammunition, Trump's odds were long and hard. At the urging of Rebekah Mercer, the megadonor's daughter, Bannon was installed to lead the campaign in mid-August 2016 following a dark national convention, rotting poll numbers and the ouster of chairman Paul Manafort.

Prior to this, Bannon didn't speak with Trump regularly, Green notes, instead using the outside game to bolster him, by battling Fox, churning up information on Clinton and greasing important endorsements like that of Sen. Jeff Sessions of Alabama.

But once Bannon had his hands on the steering wheel, he promised, "It's not going to be a traditional campaign." He urged an incessant branding of Clinton as corrupt, in press releases, on the trail -- "Crooked Hillary" -- and encouraging the "Lock Her Up" chants that reverberated through Trump venues.

At the campaign's lowest ebb, when the Access Hollywood tape was revealed showing Trump making vile comments about his ability as a star to grope women's genitals, Bannon's mantra ahead of the final debate was "Attack, attack, attack, attack, attack," according to Green's account.

"It's gonna be ugly," Bannon acknowledged to another aide. "But there's a path."

It's why it was Bannon's brainchild to bring former President Bill Clinton's accusers to the debate site in Las Vegas and re-tar him as an accused rapist. It was the most blatant and desperate form of merciless political warfare, but it helped neutralize a negative cloud around Trump.

Green reports that in watching the women who accused Bill Cosby of sexual assault, Bannon learned on-camera testimony was powerful because his victims were attacked decades earlier "and were now elderly women and thus inherently sympathetic."

"We're going to turn him into Bill Cosby," Bannon said of Clinton. "He's a violent sexual predator who physically abuses women who he assaults."

Trump, of course, ruthlessly attacked the former president during that third and final debate. ("Darkness is good," Bannon counseled Trump.) Four days later, Trump's slumping numbers began to recover.

Trump's private polling continued to move in the right direction but Bannon was still dogged by a nagging question of why Clinton wasn't campaigning in Midwestern battleground states where he was tracking his candidate's gains. Why didn't they see what he did?

Only when Election Night unfolded did it dawn on Bannon that Clinton had made the same foolish mistake as the Republicans who tried to defeat her in the past: She'd become so intoxicated with the righteousness of her cause, she became trapped in her own bubble.

The result: The most staggering upset in political history, with the makings of a Hollywood movie.