Retired neurosurgeon Ben Carson has surged to the No. 2 spot in the GOP field, overtaking former Florida Gov. Jeb Bush and, combined with front-running businessman Donald Trump, gives outsiders a firm grip atop the Republican presidential race. Combined, the two men have 40 percent of the vote in the latest Quinnipiac University Poll. Add in businesswoman Carly Fiorina’s 5 percent, and nearly half of Republicans say their No. 1 choice for president is someone who has never won a public election. But it’s Mr. Carson’s swelling support that stands out. “He’s the safe rebel,” said Michael McKenna, a GOP...