Chicago Tribune's John Kass has a humorous column on Barack calling a female reporter, "sweetie," and not answering her question; there's also a link to the video.
Barack's official response is that he has a "bad habit" of "calling people sweetie." But, really, it's not "people" that get called this diminutive, only women. It's OK to call children "sweetie," but not for a presidential candidate to say that to a reporter asking a question. In this case, the reporter seems to yell out her question while Obama is doing a photo-op at a factory. She's disturbing the peace by asking her question, by putting him on the spot. So Obama's using this dimunitive is a macho way of not answering a question, or quieting a woman.