Usually, you have to wait until a person becomes president to see if they can fulfill the promise of their presidency. But Donald Trump is offering us a sneak preview. He has promised unrivaled success as president, even though he has no political experience. His campaign tests this proposition. Trump had no experience as a campaigner either, yet he beat 16 rivals soundly, causing some of them to embarrass themselves, perhaps irrevocably. The general election, though, has posed a stiffer challenge.