Voters encountering Elizabeth Warren on the presidential campaign trail these days often seem surprised. After a packed gathering at an elementary school in Concord, N.H., in April, a 40-something woman told me she had expected Warren to be more like Hillary Clinton but found them miles apart. A college student who caught Warren’s speech in Hanover said he was perplexed to learn that a woman once described by the U.S. Chamber of Commerce’s political director as a “threat to free enterprise” in fact believes in entrepreneurship and markets. And at an event in a Portsmouth high school cafeteria, a retired...