Barack Obama could be excused for believing two weeks ago that he had nothing more than a flower-strewn path to the nomination. Women fainted in his presence, the media loved telling the story of the new Bobby Kennedy, and Hillary Clinton appeared to have all but conceded in her last debate. A funny thing happened on the way to Obama’s coronation, however — suddenly people started treating him as a candidate rather than a secular messiah, and Obama displayed a surprising glass jaw.Now he faces an unexpected stumble, losing three of four primaries after a string of victories that should...