U.S. Democrats set high bar for supporting Obama on trade

By David Lawder and Richard Cowan PHILADELPHIA (Reuters) - Senior Democrats in the House of Representatives said on Thursday they would insist President Barack Obama provide hard evidence that proposed free trade deals will boost median U.S. incomes, laying out tough terms to support his trade agenda. The demands, hours before Obama's address to a House Democratic retreat, are part of a renewed focus by the party on middle-class economic issues. Republicans have made free trade a top priori