Democratic presidential front-runner John Kerry (news - web sites) received the endorsement of the 13 million-member AFL-CIO labor coalition on Thursday, a move that could help him rebut rival John Edwards (news - web sites)' challenge on jobs and trade. "Today we know the time has come to unite behind one man, one leader, one candidate," said John Sweeney, president of the AFL-CIO, an umbrella organization of 64 unions. "Throughout his distinguished political career John Kerry has been a friend of working families." Outside AFL-CIO headquarters two blocks from the White House and beneath a huge sign reading "America Needs...