Many Americans believe a lot of dumb, crazy, destructive, provably wrong stuff. Lately this is especially (though not exclusively) true of Donald Trump voters, according to a new survey.

The survey, from the Economist/YouGov, was conducted in mid-December, and it finds that willingness to believe a given conspiracy theory is (surprise!) strongly related to whether that conspiracy theory supports one’s political preferences.

Remember Pizzagate? That’s the bizarre theory that Hillary Clinton was helping run a child sex slave ring out of a D.C. pizza joint, as allegedly proven by code words in hacked Democratic emails.

Lest you think this theory was espoused by only a handful of Internet nutjobs, observe that nearly half of Trump voters believe it’s true. This result is based on a poll conducted after a North Carolina man burst into the restaurant with an assault-style rifle, leaving only when he was satisfied that no child sex-slaves were harbored there.

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
About half of Trump voters also believe that President Obama was born in Kenya, even though their once-birther candidate has since disavowed this conspiracy theory:

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
Another conspiracy theory still held by the president-elect is that millions of illegal votes were cast in the recent election. About 6 in 10 of his own voters agree with him. Surprisingly, about a quarter of Clinton voters agree, too.

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
Trump voters are unlikely to buy the U.S. intelligence community’s assessment that Russia hacked Democratic emails in order to help elect Trump, a view widely held by Clinton voters:

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
But on the other hand, about half of Clinton voters also believe that Russia tampered with vote tallies to help elect Trump, a theory that the Obama administration has repeatedly said there’s no evidence to support. This poll result is yet more proof that waning trust in the integrity of the democratic process is bipartisan, and that liberals should maybe keep any smug comments about paranoid, evidence-ignoring Trumpkins in check.

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
Alarming shares of both Trump and Clinton voters also believe that vaccines cause autism, despite the medical community’s reviews finding no connection(and the many outbreaks resulting from refusals to vaccinate children).

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
Conspiracy theories are hardly the only arena in which Americans have proven themselves ill-informed. The same survey also found that, astonishingly, about a third of respondents believe the share of Americans without health insurance has risen in the last five years. Even a sizable chunk of Clinton voters (21 percent) believes this.

Source: The Economist/YouGov poll, which surveyed 1,376 U.S. adults between Dec. 17-20. Numbers may not sum to 100 percent due to rounding.
In fact, the uninsured rate has fallen precipitously, and now stands at an all-time low. (This is true even when you look at only the non-elderly population.)

Source: Centers for Disease Control and Prevention, National Center for Health Statistics, National Health Interview Survey, 1997–June 2016, Family Core component.
Some of these misperceptions and false beliefs may seem laughable. To me, they’re terrifying. They result in misused resources, violence and harassment, health risks, bad policy, and, ultimately, the deterioration of democracy. Good governance becomes more challenging when Americans live in parallel universes of facts.