NORTH CONWAY. N.H.—Vivek Ramaswamy isn’t making much of a dent in the polls yet, but judging from the audience reaction at a packed Masonic lodge in Wolfeboro, New Hampshire, it won’t be long. Everyone was paying close attention. There was no sense in the room of skepticism over why this 37-year-old guy—out of nowhere and standing there with his doctor wife—had the temerity to run for president. They got it. He had done his homework and then some. Several people during the lengthy question session prefaced theirs with “I voted for Trump but I’m going to vote for you.” Others...