A Fringe Conspiracy Theory, Fostered Online, Is Refashioned by the G.O.P.

Inside a Pittsburgh synagogue in 2018, a white man with a history of antisemitic internet posts gunned down 11 worshipers, blaming Jews for allowing immigrant “invaders” into the United States.

The next year, another white man, angry over what he called “the Hispanic invasion of Texas,” opened fire on shoppers at an El Paso Walmart, leaving 23 people dead, and later telling the police he had sought to kill Mexicans.