Republican presidential hopefuls field questions posed by YouTube users. Anderson Cooper moderates. Candidates expected to take part: former NYC mayor Rudy Giuliani; former governor Mike Huckabee (Ark.), Rep. Duncan Hunter (Cal.), Sen. John McCain (Ariz.), Rep. Ron Paul (Texas), former governor Mitt Romney (Mass.), Rep. Tom Tancredo (Colo.) and former senator Fred Thompson (Tenn.) From St. Petersburg, Fla.