Left-Wing Misinformation Is Having a Moment

Several elected officials, along with a top political aide for the billionaire Reid Hoffman, recently suggested, without proof, that former President Donald J. Trump may have staged an attempt to assassinate him in July.

Mark Hamill, an actor and advocate for Democratic causes with more than five million followers on X, criticized a conservative policy proposal by railing against ideas that were not part of the document.

And last month, Vice President Kamala Harris’s presidential campaign misleadingly suggested, in posts viewed millions of times, that Mr. Trump was confused about his whereabouts during a campaign stop. Her followers seized on the posts to claim that Mr. Trump was suffering from cognitive decline.

For years, the discussion about misinformation online has focused on falsehoods circulating on the American right. But in recent weeks, a flurry of conspiracy theories and false narratives have also been swirling on the left.

Some misinformation researchers are worried that the new spate of left-leaning conspiracy theories could further polarize political discourse before the November election. More than one-third of President Biden’s supporters believed the assassination attempt may have been staged, according to a poll in July by Morning Consult.

“I don’t anticipate that we will collectively become less conspiratorial,” said Adam Enders, an associate professor of political science at the University of Louisville. “If anything, the closer we get to Election Day, the more it’ll increase.”