Mitt Romney's announcement that he will not run for president in 2016 has brought the field of candidates into focus. Is Jeb Bush really the frontrunner now? Wisconsin Gov. Scott Walker impressed audiences in Iowa last week, but so did Texas Sen. Ted Cruz. Who will emerge as the favorite among the grass roots? Rand Paul has a passionate core of followers. Will a foreign policy vision that some view as isolationist be a turnoff to voters? Lurking in the background is Hillary Clinton. Which GOP contender would fare best against her? We will cover all angles of the field for the next presidential race.