There’s something unusual about every Donald Trump rally, in the sense that it’s strange for a politician who won office relatively recently to keep holding campaign rallies.

But Trump’s most recent rally, in Tampa, Florida, on Tuesday night, was unusual even by his standards, with a sudden proliferation of attendees wearing T-shirts and signs touting the QAnon conspiracy theory.

While “Q” adherents have been on prominent display at earlier rallies, the group achieved critical mass in Florida, triggering a slew of mainstream media coverage.

Not even really coherent enough to be called a “conspiracy theory”, QAnon is a kind of interactive fan fiction for the far right in which Trump is a heroic figure arrayed against Hillary Clinton, Barack Obama and the “deep state”, which includes all the recent past presidents, who are said to have hatched a criminal plot to start wars and traffic drugs and humans for money. Updates in the story happen when an anonymous figure calling itself Q leaves “crumbs” online for fans to decode.

Any reader interested in the particularities of the Q soup is directed to this concise summary. Suffice it to say that QAnon has a wide enough following to deliver millions of views on YouTube and, now, make news at a Trump rally.

As fantasies go, it is not nearly as popular or as damaging as, say, climate change denialism, but it is a lot more colorful.

QAnon can also seem more ominous. It bears a striking resemblance – and seems to have partially sprung from – a previous wild conspiracy theory that thrived in the Trump ecosystem, the so-called #Pizzagate story, which culminated in a brainwashed adherent concerned about pedophilia firing an assault rifle in a Washington DC pizza parlor.

The QAnon phenomenon, too, has potential for violence. In June, an armed man spouting Q-nonsense used an armored truck to block traffic on the Hoover Dam. No one was hurt and the man was arrested. Last week, a suspicious man was photographed outside the office of Michael Avenatti, lawyer to Stormy Daniels. Avenatti, who figures as an antagonist in the infinitely flexible Q universe, asked for help in identifying the man to police.

The Trump rally in Tampa with so many QAnon adherents in attendance also featured an unusually unpleasant confrontation between attendees and the CNN anchor Jim Acosta. “I’m very worried that the hostility whipped up by Trump and some in conservative media will result in somebody getting hurt,” Acosta wrote afterward.

The White House on Thursday refused, through the press secretary, Sarah Sanders, to deny that the press was the enemy of the people, a portrayal championed by Trump and taken as gospel in the QAnon universe.

A Trump supporter holds up a QAnon sign in Tampa. Photograph: Rod Millington/EPA

That refusal further cemented a basic feature of QAnon: its symbiosis with Trump and the Trump movement. If this weren’t plain from the centrality of Trump in the QAnon ontology, or from the “Q” T-shirts and posters at Trump rallies, it is plain from the fact that QAnon is only the latest wild conspiracy theory to flourish under Trump.

QAnon is not more outlandish than Pizzagate. But is it more outlandish than the idea Barack Obama is a Kenyan-born Muslim, or that Democrats want to give “illegal immigrants” the right to vote, or that there were “millions of people who voted illegally” in the 2016 election, or that 17 Angry Democrats are plotting with Bob Mueller to take down Trump?

Trump promotes all of those conspiracies, and in even the wildest cases, such as the “millions voted illegally” charge, half of Republicans tell pollsters that they think that, too.

Before Trump, the far- and not-so-far-right expended a lot of energy looking for a crime in the fog of conspiracy surrounding the 2012 deaths of four Americans in Benghazi, Libya. The conspiracy theories were given official platforms by Republicans in Congress and endless fuel by rightwing media, especially Fox News.

In his book Devil’s Bargain, the journalist Joshua Green described how Trump’s former strategist, Steve Bannon, incorporated the so-called “alt-right” – and other toxic mixes of hatred and bigotry that bubbled up on the 4chan and 8chan online message boards, on Reddit and on Tumblr – into the Trump movement.

“Darkness is good,” Bannon is quoted as saying. In response to Republican resistance to Trump’s candidacy, Bannon declared, “Pepe’s gonna stomp their ass,” referring to the cartoon adopted by white supremacists as a mascot.

So in May 2016 it was Pepe. Later in the campaign, it was GamerGate, a forum for misogynist online assaults that bore an insult beloved of Trump supporters, “cuck”. In December 2016 it was Pizzagate. Now it’s summer 2018 and it’s QAnon.