Washington | Within days of former president Donald Trump vilifying immigrants on national television with false stories about Haitian migrants eating pet dogs and cats in an Ohio town, someone began threatening to blow up schools, City Hall and other public buildings, forcing evacuations and prompting a wave of fear.

Days later, authorities said, a man who described himself online as a disaffected former Trump supporter made his way with a semiautomatic rifle to the former president’s Florida golf course, evidently looking to take a shot. He was thwarted only when an observant Secret Service agent spotted him and opened fire first.