I think Bill Clinton was described as an underdog when he won his parties nomination although he had far more name recognition at the time than Duncan Hunter does now.
Yes, Bill Clinton was an underdog. He benefitted tremendously from Mario Cuoumo deciding not to run. and also from a last-second loan from a Jackson Stephens-owned bank, as I recall. However, the Democrat Party , being the closest thing America has to a party of social and political revolutionaries, is more apt to have a chaotic nominating process. Washington Republicans, at least, tend to be as far from revolutionary as possible, so our nominations are much more predictable.
I think this is a bad thing. Our primaries are so frontloaded that, frankly, there is no chance for a guerilla campaign to capture the nomination behind the backs of the establishment. The primary system was designed to ensure that only Washington, corporate-approved candidates could win, because of the upfront cash requirement of the primary campaigns.
I believe Morton Blackwell once said that if the current primary rules existed in 1976-1980, ronald Reagan would not have been elected President.