People like kade (and the Elizabeth Warren fans) forget that president is the one office that is voted on by the entire country. Senators are voted by state, representatives by neighborhood, but a presidential candidate from only one portion of one party will never get more than 25% of the vote.
A coalition of two or three groups (at least!) is necessary to win a nationwide election.
Elizabeth Warren has not more of a chance than Ted Cruz does. Both parties are seriously lacking in charismatic candidates that can unite different constituencies.
That's why Rand Paul is so scary: Despite his previous positions, he is going for the youth vote that Obama corralled. If he puts them together with the small-government anti-tax brigade, the isolationist America-Firsters and a portion of the old-establishment Republicans, those young people could deliver him a landslide.
And young people can be very gullible...