Simply put; He's the real deal!
What you see and hear is what you get. What he says is what he believes, not what you want to hear be he in New England, in the Deep South, Midwest, or Hollywood.
When he speaks he speaks from both the head and heart and that's unusual in American politics. It probably happens once in a few lifetimes.
His message is simple; Americans are being screwed and he wants them to join him in putting a stop to it.
His solution is also simple; in order to do that will require a "political revolution." No more putting band aids on a gushing wound. The revolution is not about torches and pitchforks, but about votes. One vote-one person, multiplied millions of times is a "yuuuuge" weapon if you make your vote count by using it.
His support comes from those who have been shut out of the political Establishment which is made up of the "Romney 47%", the "First-time voter", the "discouraged voter" who stopped going to the polls because there was no-one to vote for who represented them. Those who are members of the shrinking "middle class" and those who are waking up to the reality that the system is "rigged" against them.
That's who Bernie Sanders speaks to them (NOT Wall Street bankers) , and that's who will get him elected in November.