This past week, Donald Trump committed an act of casual, appalling cruelty against some of his most passionate supporters.

At a news conference Wednesday, Trump was given an opportunity to comment on the deranged conspiracy theory and loose movement known as QAnon, which posits that (deep breath now) the world is secretly run by a shadowy cabal of elite Satan-worshipping cannibal pedophiles — adherents typically count Hillary Clinton and George Soros as members — who extract powerful drugs from the glands of tortured children, concealing their insidious activities via their dominion over Hollywood, the news media, and the “Deep State.” Trump himself occupies a central role in QAnon’s mythos, cast as the unlikely savior who will finally, any day now, shatter this dastardly cabal in a vaguely eschatological grand offensive reverently dubbed “The Storm.”

Updates on Trump’s top-secret Plan against the cabal are, for some reason, provided to the faithful via cryptic communiques on fringy Internet message boards, posted by the eponymous Q, who purports to be a highly-placed Trump administration insider. There’s plenty more — QAnon canon is as baroque as any comic book continuity — but you get the drift. There is, needless to say, no actual evidence for this bizarre fantasy.

When Trump was asked to weigh in on this burgeoning movement, the right answer should have been simple and obvious: “Q is not real; anyone who buys into this hoax is being taken advantage of.” But Trump failed this embarrassingly basic test of honesty and decency.

First, he claimed (implausibly) to be unfamiliar with the movement’s theories, but praised them as patriots. Then, when pressed on their central doctrine — the belief that he is “secretly saving the world from this satanic cult of pedophiles and cannibals” — he offered what sounded to believers like a winking confirmation. “I hadn’t heard that,” he replied, “but is that supposed to be a bad thing? If I can help save the world from problems, I’m willing to do it, I’m willing to put myself out there. And we are actually, we are saving the world from a radical left philosophy that will destroy this country.” QAnon adherents were over the moon.

To see how truly reckless and damaging this was, it’s important to understand that QAnon is not a harmless delusion. The FBI last year assessed that QAnon and similar theories present a genuine threat, probably to inspire “both groups and individual extremists to carry out criminal or violent acts.” Indeed, they have already done so on multiple occasions, as the Combating Terrorism Center at West Point has documented. One QAnon adherent will soon face trial for kidnapping her children from foster care under the false belief she was “saving” them from the sinister cabal. Another apparent QAnon adherent was arrested after she attempted to ram her car into the vehicles of strangers who she imagined were pedophiles. Another endangered his own children by leading police on a high-speed car chase — which he streamed online while pleading for QAnon and Donald Trump to save him.

QAnon, a baseless conspiracy theory, is fueled by right-wing outrage online and in the real world. (Elyse Samuels/The Washington Post)

Only a handful of the many thousands of QAnon believers are disturbed enough to endanger others so dramatically. But many, many more are effectively destroying their own lives in quieter ways, sacrificing ties to friends and family as they chase Q’s clues down an online rabbit hole. The “QAnon Casualties” group on the Web forum Reddit, which now boasts nearly 19,000 members, is a heartbreaking catalogue of ruined relationships: friends and loved ones “lost” to the cult of Q, descending ever further into fear, anger and paranoia as their detachment from reality alienates husbands from wives and parents from children and grandchildren.

The spread of QAnon also threatens to damage the Republican Party as a whole. The upcoming election will see several professed Q believers running on Republican tickets — one of whom, Marjorie Taylor Greene, is in such a solidly Republican district that she’s all but guaranteed to win a seat in the House of Representatives. The Texas Republican Party has openly employed QAnon slogans and iconography. And Trump’s endorsement, broadcast on national television from the White House, is bound to send a fresh crop of his supporters on an expedition into the fever swamps.

Trump — by dint of his central place in QAnon’s mythology — is in a unique position to put the brakes on all of this. To be sure, the most hardcore true believers would probably be undeterred even by a clear disavowal from the president. We’ve already seen numerous dramatic QAnon prophecies — Hillary Clinton’s arrest imminent! Robert Mueller secretly working with Trump against the evil cabal, with the Russia investigation as an elaborate cover! — whose failure to come true was quickly rationalized away by the devout. But some would probably snap out of it and begin piecing their lives back together. And halting the Republican Party’s institutional flirtation would at least slow the spread of the virus to new victims.

It would take almost no effort from Trump — a few sentences — to mitigate the damage QAnon is doing to both his party and his most ardent fans. It would cost him almost nothing politically: Most of the folks lost in the QAnon funhouse were probably Trump supporters before they stumbled in, and they’ll surely remain supporters after they’re led out. Yet it seems clear that, at least absent strong pressure from fellow Republicans, Trump has no intention of doing the right thing. His ego, apparently, is so satisfyingly stroked by QAnon’s worship that he’s willing to let his party further humiliate itself, and his own admirers wreck their families, rather than say anything to dispel a fantasy in which he is cast as the messiah.

That may not be as grotesque or dramatic as drinking the blood of children, but it is certainly a sort of human sacrifice.