Citizen Cruz: Trump hammers away, Senate leader mum

By Doina Chiacu WASHINGTON (Reuters) - Republican presidential front-runner Donald Trump on Sunday hammered away at his closest challenger's eligibility to be U.S. president, while the party's Senate leader said the chamber will stay out of the fray involving Ted Cruz's citizenship. Under the Constitution, presidents must be "natural born citizens." Cruz was born in Calgary, Alberta, to an American mother, which he says makes him eligible to run. Senate Majority Leader Mitch McConnell told ABC's