In reality, Bannon has been a guiding figure for Trump for years as the New York developer began seriously to consider running for president, according to associates of both men.
Sam Nunberg, who said he arranged numerous telephone calls between Bannon and Trump dating to 2013, said it did not take long for the two to become ideological soul mates. At a time when Trump was widely dismissed as a credible candidate, Nunberg said, Bannon took him seriously and publicized him on the Breitbart News website, which Bannon oversaw.
From those earliest days, Bannon encouraged Trump to run for the White House, and then, in the race's final months, he effectively took over a campaign that appeared to have almost no chance of succeeding.
"The only candidate who could have won this past election on the message of populism and conservative nationalism is Donald J. Trump," said Nunberg, who worked for Trump as a political and public affairs adviser before he was fired in 2015. "However, at the time Steve took a formal role, the campaign was in dire straits, and I don't believe the president would have been able to pull off that upset at the end without Steve Bannon."
It is possible, if not likely, that Trump and Bannon will reunite again soon — the president has a long history of making up with associates against whom he has lashed out. But for now, at least, Trump and Bannon are on the outs, following revelations in a new book by Michael Wolff, "Fire and Fury: Inside the Trump White House," in which Bannon is quoted as saying that Donald Trump Jr.'s meeting with a Russian lawyer at Trump Tower in June 2016 was "treasonous."
Bannon declined to comment Wednesday.
John Thornton — a former co-worker of Bannon's at Goldman Sachs whom Bannon has described as a "mentor" — saw Bannon work closely with Trump during the transition and the early months of the administration. He said in an interview Wednesday that he was impressed at how smoothly they got along and by how the president listened closely to Bannon's advice on issues ranging from the economy to China.
"It was a very healthy, highly engaged, intimate relationship that you would expect to see between the person who had just won the presidency and the person who had run the campaign," Thornton said. "There's no question he was clearly a central figure helping the president achieve his goals."
Bannon and Trump were introduced in 2010 by David Bossie, who rose as a hero on the right when as a congressional staffer in the 1990s he helped to investigate Bill Clinton and went on to become president of Citizens United, a conservative group whose work includes a movie pillorying Hillary Clinton. Bossie did not respond to a request for comment.
Outwardly, the two did not seem to have much in common — one making his fame and fortune in front of the cameras, the other building a power base behind them.
Trump cared deeply about his looks, his clothing and his hair, and he promoted himself in his reality television show, "The Apprentice." He had toyed with the idea of running for the presidency since 1987, but had always backed down when he concluded he had no chance of winning.
Bannon had a wild-looking demeanor, often dressed shabbily, uncombed and unkempt, despite his background in the Navy, Harvard Business School and Goldman Sachs. He made millions of dollars working in Hollywood for his boutique firm, Bannon & Co., on a variety of investments, as well as the sale of television properties that wound up giving Bannon a payoff from Seinfeld reruns. He made deals around the world, profiting from the globalism he later demonized. He produced films that criticized Wall Street, the political establishment and "Islamic fascism," and he gave speeches around the country promoting the tea party agenda.
The two men bonded over their rare ability to be members of the coastal elite while representing themselves as champions of the downtrodden working class — as well as over a shared anger at the Republican establishment.
That bond gelled shortly after Mitt Romney lost the presidential race in 2012. Trump began tweeting that Republicans had been robbed: "This election is a total sham and travesty. We can't let this happen. The world is laughing at us." Foreshadowing his campaign, Trump also tweeted: "We should march on Washington and stop this travesty. Our nation is totally divided."
During that same year, Bannon became executive chairman of Breitbart News and reshaped the website into one promoting more-nationalistic views, later declaring that it was "the platform for the alt-right." Bannon's Breitbart attracted white nationalists, although Bannon denied accusations that he was fomenting racist views.
It was after the 2012 election, as Trump went through his quadrennial exercise of pondering a bid for the presidency, that he began talking to Bannon on the phone more regularly. By 2015, their conversations became public, as Trump took turns as a guest on a radio broadcast called the Breitbart News Daily. Bannon has said that he was "mocked and ridiculed" for talking about a Trump candidacy on the show but that he realized that Trump had an uncanny ability to attract support.
During the radio interviews, Bannon sometimes seemed to be tutoring Trump about how to frame issues. For instance, in one interview, Trump said he wanted to build a border wall but allow some immigrants who graduated from U.S. universities to stay in the country.
"I still want people to come in. But I want them to go through the process," Trump said.
Bannon responded, "You got to remember, we're Breitbart. We're the know-nothing vulgarians. So we've always got to be to the right of you on this."
"Oh, that's okay," Trump said.
As Trump's presidential campaign unfolded, Bannon regularly advised Trump and his son-in-law, Jared Kushner, while also pushing the candidacy on the Breitbart website. Then, as the campaign seemed headed for defeat, Trump in August 2016 hired Bannon as the campaign's chief executive, which gave him significant control over message and strategy. Just as he had on his radio show, Bannon pushed Trump to go further to the right and to hammer Democratic nominee Hillary Clinton mercilessly.
The strategy worked, and Trump rewarded Bannon by making him the White House chief strategist, a powerful role that put him in conflict with Kushner, who was named Trump's senior adviser. Bannon had worked well with Kushner during the campaign but often was at odds with him in the White House, as Bannon pushed policies such as pulling out of a global-warming treaty, which Kushner and his wife, Ivanka Trump, reportedly had supported.
Bannon announced his arrival at the White House with an attack on the media.
"The media should be embarrassed and humiliated and keep its mouth shut and just listen for a while," Bannon said in an interview with the New York Times. "I want you to quote this: the media here is the opposition party. They don't understand this country. They still do not understand why Donald Trump is the president of the United States."
That pleased Trump. But then Bannon appeared on the cover of Time magazine, with the headline, "The Great Manipulator," a portrayal of him as the brains behind the president. Trump famously collects magazine covers of himself on the wall of his office at Trump Tower, and he takes offense when others take credit for his accomplishments. The Time cover prompted Bannon's enemies in the White House to attack him. Kushner privately joined in the criticism, according to a White House official familiar with the matter.
Thornton said that while the relationship between Trump and Bannon may baffle some, there is a "larger picture" that makes sense to Bannon.
"Bannon sees himself as the head of a movement, and he sees Trump as the beneficiary of that movement at this point in time," Thornton said. "Bannon sees himself as helping Trump stay true to that movement. If Trump or his administration deviates from the movement, Bannon will go on the offense. If Trump stays true, Bannon is all in."
Another associate of both men, who spoke on the condition of anonymity, said that "no matter what the president says now, Steve during the transition and rolling forward was critically important. He was a very consistent voice of the far right . . . when others wanted to fade or fold."
The relationship seemed to have fallen apart in August, shortly after Bannon was quoted in an interview with the American Prospect saying "there's no military solution" to North Korea's nuclear capability, "they got us." Trump fired him, although Bannon said he resigned. In any case, Bannon later told the Weekly Standard, "The Trump presidency that we fought for, and won, is over. We still have a huge movement, and we will make something of this Trump presidency. But that presidency is over. And there'll be all kinds of fights, and there'll be good days and bad days, but that presidency is over."
Bannon then returned to running Breitbart News and, in effect, began laying the groundwork for the next phase of his war against the Republican establishment, of which he now viewed Trump as a captive. Still, the two remained in touch and had talked on the telephone at least five times since Bannon's departure, according to the White House. Bannon persuaded Trump to endorse Roy Moore, the failed U.S. Senate candidate from Alabama who was accused of inappropriate sexual contact with a 14-year-old girl when he was in his early 30s.
Then came the news Wednesday of Wolff's book, and the president, having played a crucial role in making Bannon one of the best-known political figures of the day, said that his former chief strategist had "lost his mind" and that he was done with him.