NEW : Des Moines , Iowa ( CNN ) -- The U.S. House is debating a bill to ban nuclear retaliation . President responds to a question at a town hall - style meeting . The dispute is a major one between the world 's two largest economies .
NEW : The U.S. House is debating a bill to ban nuclear retaliation . President responds to a question at a town hall - style meeting . The dispute is a major one between the world 's two largest economies .