Scott Walker, a likely Republican presidential contender who is riding high in polls in the early voting state of Iowa, was literally the leader of the pack on Saturday at a gathering of 2016 White House hopefuls. Walker, the governor of neighboring Wisconsin, joined U.S. Senator Joni Ernst at the head of a parade of about 300 motorcycle riders who traveled 39 miles to Ernst's inaugural "Roast and Ride," a political event combining barbecue and the roar of Harley-Davidsons.