The Republican Party under Donald Trump has habitually elevated extreme right-wing candidates who can’t find enough support outside of hardcore partisans to win elections. But Mark Robinson, who won the GOP nomination for governor of North Carolina Tuesday night, is a special case even by the modern GOP’s standards. Robinson, North Carolina’s current lieutenant governor, has hurled hateful remarks at everyone from Michelle Obama to the survivors of the Parkland school shooting. He’s called the LGBTQ community “filth.” He threatened to use his AR-15 against the government if it “gets too big for its britches,” and he wants to outlaw...