Why do half of Republicans—and two-thirds of Trump’s primary voters—remain convinced that Barack Obama is a Muslim? Because GOP elected officials and conservative leaders encouraged them for more than a decade. Trump launched his political career by embracing a conspiracy theory twisted around two deep American taproots—fear and loathing of foreigners and nonwhites. In 2011, he made himself chief spokesman for the fantasy that President Obama was born in Kenya, a fringe idea that he single-handedly brought into the mainstream. House Republicans co-sponsored a federal bill that would require presidential candidates to submit birth certificates and other proof that they aren’t secret foreigners. After the Hawaiian bureaucrat who released a copy of the president’s birth certificate died in a private plane crash, Trump tweeted: “How amazing. … All others lived”—suggesting the official had been murdered by the Obama conspiracy. Finally, in the fall of 2016, he grudgingly (and temporarily) admitted the president was indeed a native-born American—at the same moment that an Economist/YouGov survey found a majority of Republicans believed that Obama was probably or definitely born in Kenya.

“Scalia,” the right-wing radio host Michael Savage asked candidate Trump in 2016, “was he murdered … ?” Well, Trump replied, “they say they found the pillow on his face, which is a pretty unusual place to find a pillow.” On Fox and Friends, Trump discussed, as if it were fact, the National Enquirer’s suggestion that Ted Cruz’s father was connected to JFK’s assassination. “What was he doing with Lee Harvey Oswald shortly before the death, before the shooting? It’s horrible.” The Fox News anchors interviewing him neither challenged nor followed up. Trump revived the 1993 fantasy about Vincent Foster—his death, Trump said, was “very fishy,” because Foster “had intimate knowledge of what was going on. He knew everything that was going on, and then all of a sudden he committed suicide. … I will say there are people who continue to bring it up because they think it was absolutely a murder.” He has also promised he’s going to make sure “you will find out who really knocked down the World Trade Center.”