It is a case of being hoisted by his own petard.

President Trump has convinced his own supporters of the false conspiracy theory that mail-in ballots are subject to rampant fraud — so much so that Republicans are, evidently, refusing to vote by mail.

The Post’s Amy Gardner and Josh Dawsey report that Democratic voters have embraced mail ballots in far greater numbers than Republicans in primaries this year — alarming Republican strategists who say it could undercut their candidates, including Trump, particularly in states such as Florida and Arizona. In Michigan, Trump supporters actually burned absentee-ballot applications.

This is but one sign of the descent into madness that Trump has caused. Conspiracy theories, long a staple of the president’s, are spreading faster than covid-19 among his supporters, inducing mass delusion. In the most ominous manifestation, he has convinced his supporters that fears of the virus are overblown (a Democratic “hoax”), that mask-wearing is effete political correctness and that the pandemic’s spread merely proves that “our TESTING is much bigger and better.”

Now the pandemic is growing unchecked in Trump-backing states, and hospitals are running out of rooms. Tulsa, where Trump insisted on having an indoor rally, has seen a dramatic surge in cases “more than likely” spurred by the rally and protests, the local health department said.

Everywhere, it seems, reality is colliding with Trump’s fantasies. This week alone, the White House pushed the Centers for Disease Control and Prevention to revise its advice on reopening schools to fit Trump’s rosy claims; an inspector general accused the administration of undercutting public trust by forcing the National Weather Service to support Trump’s fanciful claim that a hurricane menaced Alabama last September; and a lopsided Supreme Court majority dismissed Trump’s claims of “absolute immunity” as inconsistent with “200 years of precedent.”

Trump responded Thursday with another conspiracy theory. He rekindled his unsubstantiated “Obamagate” allegation that his predecessor perpetrated “the biggest political crime and scandal in U.S. history” by trying to sabotage Trump’s campaign.

This followed Trump’s revival of an old smear saying MSNBC host Joe Scarborough “got away with murder” in the death of a former aide, Trump’s suggestion that an elderly demonstrator in Buffalo injured by police was actually an antifa agent, and his assertion that opponent Joe Biden is addled. Meanwhile, Trump’s son Eric renewed the theory that the virus is a Democratic hoax that will “disappear” after the election. And prison-bound Trump confidant Roger Stone just had more than 100 deceptive accounts and pages taken down by Facebook.

Now we see growing ruin caused by so much lunacy coming from the highest office in the land. The GOP is becoming a Garish Opera of Paranoia.

In Colorado, an incumbent member of Congress lost a Republican primary to a candidate who embraced the QAnon conspiracy theory about a “deep state” child-sex ring plotting against Trump. Believers in this craziness, who have been retweeted by Trump and display QAnon symbols at his rallies, include the party’s Senate nominee in Oregon and a Republican in a House runoff in Georgia.

A Pew Research poll last month found that by nearly two to one, Republicans are finding it harder to identify “what is true and what is false about the outbreak.” A similar proportion of Republicans — 48 percent — found it definitely or probably true that “powerful people planned the coronavirus outbreak,” while 57 percent believed deaths had been intentionally overstated. Why the confusion? Seventy-five percent of Republicans believed the White House presents accurate information.

We have been building toward this for some time, as Republican officeholders and commentators touted conspiracy theories as fact, first during the Clinton administration and then during the Obama administration: Vince Foster. Troopergate. Black helicopters. Benghazi! Hillary Clinton’s brain damage. Huma Abedin and the Muslim Brotherhood. Pizzagate.

In that sense, Republicans were primed for Trump when he proposed that Barack Obama was born in Africa, climate change is a Chinese hoax, Ted Cruz’s father aided the Kennedy assassination, Antonin Scalia’s death could have been foul play, American Muslims celebrated 9/11, Obama wiretapped Trump Tower, the Democratic National Committee server was hidden in Ukraine, Seth Rich was killed because of the DNC emails, globalists and a deep state manipulated government, millions voted illegally against him, and many more.

It was all fun and games in 2015 and 2016, when three-fifths of his supporters (according to one Democratic poll) embraced his claim that Obama wasn’t born in the United States. But now he’s convincing his supporters not to mail in their ballots and not to protect themselves against the virus.

A president disenfranchising his own supporters and jeopardizing their lives sounds like the wackiest conspiracy theory of all. But this one is true.

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