Urged on by President Barack Obama, Democratic leaders in the U.S. House of Representatives hustled on Thursday to round up support for a sweeping healthcare overhaul headed to a close floor vote on Saturday.The House drive for healthcare reform, Obama's top domestic priority, was bolstered on Thursday by the backing of the American Medical Association, which represents U.S. doctors, and AARP, the powerful lobbying group for older Americans."I urge Congress to listen to the AARP, listen to the AMA, and pass this reform for hundreds of millions of Americans," Obama said in a surprise appearance in the White House briefing room. "We are closer to passing this reform than ever before."Failure in the Democratic-controlled House would be a huge political blow to Obama, who planned to visit the Capitol on Friday for a pep talk to House Democrats before the vote.