(R-L) National security adviser Michael Flynn, and his staffers K.T. McFarland and Michael Flynn Jr. Photo: Eduardo Munoz Alvarez/AFP/Getty Images

The most frightening aspect of the looming Donald Trump presidency is not so much the likely outcomes, many of which are horrifying, as the unlikely ones. Running the federal government of the world’s most powerful country is hard, and many things can go wrong. Full control of government is about to pass into the hands of a party that, when it last had it, left the economy and the world in a shambles. These disasters occurred because the party’s ideological extremism made it unequipped to make pragmatic choices, and because its chief executive was a mental lightweight. Sixteen years after it last came to power, the party has grown far more ideologically extreme, and its head of state is much less competent. Many of the tail risks of an extremist party led by an unqualified president are difficult to foresee in advance. But one is especially glaring: the appointment of Michael Flynn to be national security adviser.

National security adviser is a crucial position for any president. It is especially so for a uniquely inexperienced one. (Donald Trump being the only president in American history lacking any public experience in either a civilian or military role.) And it is all the more crucial given Trump’s flamboyant lack of interest in getting up to speed (he confounded his aides by eschewing briefing books throughout the campaign, and has turned down most of his intelligence briefings since the election.) Flynn’s appointment is the one that contains the sum of all fears of Trumpian government.

Flynn’s portrait seems to reflect the worst qualities of Dick Cheney, but in exaggerated form. Flynn avidly subscribes to conspiracy theories. He believes Islamists have infiltrated the Mexican border en masse, guided along the way by Arabic-language signs Flynn claims to have seen himself. He also believes that Democrats have imposed Sharia law in parts of Florida, and shared a now-deleted tweet that suggested Hillary Clinton could have been involved in child sex trafficking. These claims were frequent enough that his subordinates at the Defense Intelligence Agency gave them a name, “Flynn facts,” which means a Flynn belief that is the opposite of a fact.

Compounding Flynn’s susceptibility to conspiracy theories is his professed hostility to any information that undercuts his preconceived notions. According to a former subordinate speaking to the New York Times, in a meeting with his staff “Mr. Flynn said that the first thing everyone needed to know was that he was always right. His staff would know they were right, he said, when their views melded to his.” What makes this so chilling is that it is the pathology that destroyed the Bush administration’s foreign policy, except that what for Cheney was a tragic flaw is, to Flynn, an aspirational credo.

Flynn has reinforced this method by surrounding himself with subordinates unlikely to challenge his fever-swamp convictions. His deputy, K.T. McFarland, last worked in government in the 1980s, as a public-affairs officer, and her main experience since then has been as a Fox News talking head. Foreign affairs experts in both parties described her to Politico reporter Michael Crowley as “a policy lightweight with no real personnel or crisis management experience.” One Republican told Crowley, “She is not a thinker — but, more importantly in that job, not a doer … Anyone who’s watched her show knows she’s sort of a follower, someone who gets all her talking points off the [Republican National Committee’s] Web page.”

Flynn’s other high-level appointee, Monica Crowley (no relation to Michael), is more credentialed — having gained academic training before going on to a career, like McFarland, as a Fox News ranter — but also much more crazy. Like Flynn, who has tweeted “Fear of Muslims is RATIONAL,” Crowley frames the fight against Islamist terrorists in the broadest possible terms, as a struggle between civilizations. “We are in a holy war,” she has said, repeatedly. Islamist radicals have always sought to frame the conflict in precisely these Islam-versus-the-West terms, which they see as their best tool to recruit the highest number of Muslims to their side. For the same reason, American foreign-policy experts in both parties, who want to isolate terrorists from the Muslim majority, have resisted cooperating with this notion.

Crowley, like Flynn, is driven by fervent anti-Islamic terror more than any coherent calculation. She has depicted Muslim refugees as infiltrators plotting to take over Europe, and falsely claimed the Paris attacks were carried out by Syrian refugees. She has propounded frequently about Huma Abedin’s alleged “ties to Islamic supremacists,” which even conservative columnist Jamie Weinstein, writing in the Daily Caller, called “crazy Huma Abedin conspiracy theories.” More alarmingly, she has claimed the holy war against Islamists requires violating the Constitution. “This is essentially the Constitution versus the Quran on every level. The Constitution is not built to fight this war.”

Crowley is also a devotee of birtherism and other anti-Obama fever-swamp conspiracy theories. Obama, she told radio listeners in 2008, is “not black African, he is Arab African … And yet, this guy is campaigning as black and painting anybody who dares to criticize him as a racist. I mean that is —it is the biggest con I think I’ve ever seen.” She continued defending birtherism for years. (“The birth-certificate stuff, how did he get into Columbia and Harvard, who paid for his education, all very legitimate questions.”) There are hardly any Obama conspiracy theories Crowley does not believe. The president, according to her, has “gotten w/ with bloody murder (literally. See: Fast & Furious, Benghazi).”

Perhaps the most powerful member of Flynn’s team of nutters is his son and chief of staff, Michael Flynn Jr. The younger Flynn is active on white-supremacist social media, and has tweeted out bizarre claims like “the only reason minorities voted for BO is the color of his skin and NOT for the issues,” or “soooo African-Americans can have B.E.T. but whites can’t have their own dating site? Hmmm.” Flynn also promoted the conspiracy theory that a Washington pizzeria had a secret back room with child sex slaves that was somehow connected to Hillary Clinton. When a gunman showed up there trying to liberate the imagined slaves, the ensuing publicity forced Trump’s transition team to remove Flynn Jr. from his official role on the transition team. But there’s no evidence his deep influence on his father has abated.

It is almost impossible to overstate the danger to American national security posed by the combination of Flynn and his staff. Because his appointment is not subject to Senate confirmation, and also because it has been overshadowed by the Rex Tillerson nomination and its connection to the fast-moving Russia story, Flynn has receded from the front pages. His appointment is unprecedented, like so many other other things Trump has done — indeed, the endless violations of precedent are what make Trump’s election so surreal, and its dangers difficult to order.

But it is the specific, mutually reinforcing characteristics of Flynn and his staff that invite the most alarm. He is a conspiracy theorist averse to any challenge to his suspicions, surrounding himself with a staff of fellow conspiracy theorists seemingly designed to shut out any challenge to his biases, providing advice to a novice president who is himself a conspiracy theorist. It’s under-informed, overconfident crackpots all the way down. As a comedic script, it would defy plausibility. Except there’s a terrifying chance that a lot of innocent people will die as a result.

*A version of this article appears in the December 26, 2016, issue of New York Magazine.