Julian Zelizer: What's behind the surging interest in Pete Buttigieg

It looks like Mayor Pete Buttigieg -- a married, gay millennial whom few voters had heard of until a few months ago -- now has a real shot at the Democratic nomination. Who would have thought that the mayor of South Bend, the fourth largest city in Indiana, could compete in one of the most crowded primary fields ever? Buttigieg, who is expected to formally launch his campaign Sunday, has emerged as a formidable candidate.