WASHINGTON, DC – In many, if not most, US administrations, some figure emerges who convinces the press that the president couldn’t function without him (it’s yet to be a her). The indispensable aide is, indeed, one of the most well-worn tropes of the modern presidency. Karl Rove was "Bush’s Brain”; Harry Hopkins held Franklin Delano Roosevelt’s prolific White House team together; Bill Moyers appeared on a magazine cover as "Johnson’s Good Angel.” Without such a figure, the story inevitably goes, the administration would be a mess, if not a disaster.

As often as not, the trope is invented or encouraged by the particular indispensable figure. Journalists usually fall for the story, regardless of how well-founded it is: it clarifies everything, and it gives them something to write about. The indispensable aide is only too happy to reveal some dramatic story about how he saved the day, devised some particularly ingenious idea, or prevented some terrible mistake.

But, as often as not, the soi-disant crucial figure oversteps. In the Reagan White House, Don Regan, who succeeded James Baker as Chief of Staff, fancied himself the prime minister: he inserted himself into photos of Reagan with Soviet leader Mikhail Gorbachev, was rude to lesser beings (including reporters), and made the fatal mistake of hanging up on Nancy Reagan, who was dedicated to looking after her Ronny. Regan was soon out.

Presidents themselves aren’t particularly fond of reading how some super-smart aide saved their bacon. All presidents have healthy egos – if others are so smart, why aren’t they president? The wise president-elect identifies a peacock and avoids the species from the start, or knows how to keep its feathers in check. Barack Obama was plenty pleased with himself, with reason, but such was his dignity that no super-aide emerged during his presidency. It didn’t occur to his advisers to try to outshine him.

Stephen Bannon wasn’t particularly wise as a White House aide – he couldn’t contain his inner peacock – and Donald Trump’s ego is particularly fragile. Both are or were misfits in their roles. Trump had spent his business life surrounded by family and flunkies: no stockholders or vice chairmen with their own ambitions. The two men were a mismatch made in White House hell.

As a candidate, Trump went with his instincts, and his instinct in the 2016 presidential race was that blue-collar workers and others who feared for their economic future needed their own victims, be they Mexican immigrants or billionaire bankers. A wall – phantasmagorical or not – would keep out the "bad people” Mexico was "sending us.” As it happened, of all the people around Trump, Bannon most matched these views. A person like Bannon – who presents himself as a learned figure and confirms one’s own brilliance – is a person one wants to have close by.

Trump is essentially a "whatever works” kind of guy. Once elected, he brought in billionaires to populate his cabinet, and so far seems to have gotten away with telling his supporters that really rich people are needed to run the country.

Bannon, on the other hand, wrapped himself in what might be loosely termed a philosophy, which consisted of a nihilistic anger toward any "establishment.” But his was faux populism: while Bannon politically championed blue-collar workers, he lived on the millions he had attained from a stint at Goldman Sachs and through a fortunate investment in the TV comedy series "Seinfeld.”

He also flourished with backing from the billionaire Mercer family. The Mercers, who made their fortune through the high-tech genius of patriarch Robert Mercer and a hedge fund he led, fund Breitbart News, a far-right website formerly edited by Bannon that promotes ultra-nationalism and white supremacy, with a whiff of anti-Semitism.

Bannon’s ostensibly radical views were dressed up in a fancy set of principles embroidered with name-drops of far-out thinkers. In trade and immigration, for example, Bannon’s acquired philosophy aligned with Trump’s political opportunism (Trump’s more liberal, often Democrat-backing former self is another story).

It was a mistake to see Bannon as Pygmalion to Trump’s Galatea, or, as some did, as the Trump White House’s Rasputin. Bannon reinforced the nationalist inclination that led Trump to overrule his daughter Ivanka and his economic advisers by withdrawing from the Paris climate agreement. And Bannon intruded on foreign policy by getting himself put on the National Security Council for a while, until two of the generals in Trump’s administration – National Security Adviser H. R. McMaster and John Kelly (now the chief of staff) – got him removed. (Bannon was believed to be behind the recent push to force out McMaster, mainly by suggesting that he is "anti-Israel.”)

But Bannon’s role as genius-without-portfolio – in which Trump indulged him, until Kelly arrived and clarified chains of command – was his undoing. Without any defined responsibilities, he intruded where he wished – and ended up with a lot of enemies. He had plenty of time to fight internal battles by feeding reporters stories about his White House rivals, though he would switch someone (for example, former Chief of Staff Reince Priebus) from rival to friend, as convenient.

Bannon was a troublemaker as much as a policymaker – and the two roles didn’t mesh. Trump also began to see Bannon as a "leaker.” And Trump’s White House is all too leaky: many who work there let reporters know that they have, at best, mixed feelings about working for Trump, but believe the better part of valor is to stay and protect the country from his leadership.

Bannon’s braggadocio took him to the most dangerous terrain on which to confront Trump: the president’s obsession with his election victory. The ambiguity of winning the Electoral College vote (not, as he has falsely claimed, by the greatest margin since Reagan) but losing the popular vote by nearly three million votes, dogs Trump. That’s why he invented millions of "illegal” voters and had maps printed showing the states he won in red – covering most of the territory of the United States – even suggesting to at least one reporter that his newspaper run the map on the paper’s front page.Suggestions by Bannon that he played a major role in Trump’s election victory were poisonous to the relationship between the two men. And so this White House misfit finally had to go.

Now that Bannon is gone, however, he will hurl missives from his new-old perch at Breitbart, to which he returned the same day as his announced departure. And Trump will still be Trump.

Elizabeth Drew is a regular contributor to The New York Review of Books and the author, most recently, of Washington Journal: Reporting Watergate and Richard Nixon’s Downfall.

Copyright: Project Syndicate.