The fact that Ruth Bader Ginsburg is alive and well completely failed, in late January, to stop a conspiracy theory bubbling up. First on anonymous message boards like 4chan, and then on Twitter, Youtube, Reddit, and Facebook; people were spreading that the 85-year-old US Supreme Court Justice had secretly died. There was a cover-up, the theory claimed, and she had been replaced with a body double. It was boosted by – among others – a former Trump aide, Seb Gorka, and Hollywood actor,James Woods.

“Still no sign. 6 days left until Ruth Bader Ginsberg has to make her official appearance at @realDonaldTrump’s State of the Union,” Gorka, a radio host and regular conspiracy theory pusher who served as a deputy assistant to the president tweeted. (Asked about his tweet by the Daily Beast, Gorka responded by inviting the reporter to “go outside and lick a metal street lamp.”) #WheresRuth trended. On 21 January, Fox News accidentally broadcast her obituary.

Despite this furore, Justice Ginsburg returned to America’s highest court on 19 February, after surgery to remove two cancerous nodules from her lungs. “She doesn’t smile that often on the bench,” Mark Walsh, who writes the View from the Courtroom column for SCOTUSblog, tells me. That first day back, though, “She did smile, sitting up straight and really diving into the questions.”

Because the Supreme Court has consistently rejected the idea of televising its deliberations, however, Ginsburg’s return to the court couldn’t snuff out the conspiracy entirely, and it still lingers. It touched a nerve – got people rattled – because Ruth Bader Ginsburg occupies a unique and exalted position in the American political and cultural psyche.

Before Bill Clinton nominated her to become the second female Supreme Court Justice in history, she was already a giant. As general counsel for the American Civil Liberties Union (ACLU) in the 1970s, she had been instrumental in bringing cases that guided the court toward ruling that gender-based discrimination was covered by the “equal protections” clause of the 14th Amendment to the Constitution. She was a ruthless, methodical strategist, sometimes bringing cases where the victim of discrimination was male, rather than female, to ease the all-male court gently round to her way of thinking.

Even her extraordinary career doesn’t explain the iconic status of “Notorious RBG” – a nickname made famous on a hugely popular blog dedicated to Ginsburg memes and news which later became a bestselling book. Two movies about her have come out in the last year alone. She is the subject of a recurring segment on Saturday Night Live gifting her the catchphrase “That’s a Ginsburn!” Even her workout routine is famous: Ginsburg, who is 85 and weighs 100lb, can reportedly bench-press 70lb. When Late Night host Stephen Colbert joined her in the gym for a segment last year, Ginsburg wore a t-shirt that said “Super Diva.”

When you ask American progressives their worst political fear, they’ll often just grimace and say: “RBG.” Everyone knows what that means. The public adoration hides an uncomfortable truth: everyone is acutely aware that Ginsburg’s biggest legacy may yet be her death, which could act as the tipping-point for the end of American democracy. Trump has already filled two Supreme Court seats, but both were previously occupied by conservative justices – very conservative in the case of Antonin Scalia (though he and Ginsburg, famously, formed an unlikely friendship across their ideological gulf), more moderate in the case of Anthony Kennedy.

Ginsburg, though, is a different matter. “If Justice Ginsburg were to leave the court for any reason under President Trump, that would shore up a conservative majority on the court for generations,” Walsh says. Appointing her successor would allow the president to change the Supreme Court beyond recognition, potentially making it next to impossible for future presidents to undo the damage he wreaks.

The terror this possibility induces on the left makes Ginsburg an enticing target for conspiracists and trolls. But the theory about her death sprung – importantly – from the same places as a much larger theory known as “QAnon,” a labyrinthine web of ideas, symbols, and lurid fantasies. During the 2016 election, its antecedent, “Pizzagate” – a conspiracy theory centred around the idea that Hillary Clinton and several of her advisers were running a child sex ring out of the basement of a pizzeria in Washington, DC – became headline news when an armed believer turned up at the restaurant with an assault rifle.

QAnon flowered in the same online communities, but it is more complex than Pizzagate – an all-encompassing conspiracy worldview. In brief, its subscribers believe the Mueller investigation is in fact secretly focused on a paedophile cabal led by Obama and the Clintons, and that Trump is giving the investigation cover so the “deep state” can’t shut it down. Originating as a set of cryptic posts on the anonymous message-board 4chan in 2017, QAnon has become a vast and arcane lore.

Anonymous image-posting forums like 4chan – which has enormous influence thanks to its more than 22 million users per month – are fertile soil for conspiracies to grow. This is partly because there is no way of telling whether another user is telling you something true, or something that they believe to be true, or when they are “trolling” – the art of stringing a sucker along just for the hell of it.

Because QAnon is part-conspiracy theory, part-fandom, and part-mass live-action roleplay, it is hard to know who’s taking it seriously and who’s stringing the others along for laughs – but some certainly believe it. QAnon signs have started appearing at Trump rallies. Last June, a Marine Corps veteran taken in by the ideology got into an armed 90-minute standoff with police in Arizona. The communities pushing that ideology – part of an ideological feeder-system which feeds into the White House not just through Gorka, but through people like Alex Jones, on whose show Trump has been a frequent guest – have now integrated it into their canon.

Ginsburg, who was forced into a staggeringly rare apology in 2016 for condemning Trump in public, seems now to have settled more comfortably into the role of nemesis. The day she returned to the bench, Walsh says, she was “just happy to be back at it … as excited as an 85-year-old probably gets”. Linda Hirshman, whose book Sisters in Law charts the lives of Ginsburg and Sandra Day O’Connor, the first two women to sit on the Supreme Court, tells me she thinks Ginsburg sees herself as fighting a “rearguard” action now.

“If she can hang on to fight that rearguard action, not give the seat over to those villains, then [she feels] she will have done a lot in her life,” Hirshman says.