And he was running for president of the US, but dropped out of the race recently.

He is, however, still on the Ballot, and Democrats can still vote for him to be their candidate. If he gets more than 15% in any state, he will add delegates to his (approx) 200 that will represent him and his agenda at the National Convention of the party. I'd suggest that anyone who really likes Dean's policies should do that. Those delegates will not affect who the eventual winner will be, but they WILL bring Dean's progressive agenda to a more prominent position at the convention and thereby influence the party's agenda.