WASHINGTON, June 18 (UPI) -- A new television ad blasting likely Republican presidential nominee John McCain is only the beginning of liberal "independent group" ads, union officials say. The spot, produced independently of Illinois Democratic Sen. Barack Obama's presidential campaign, financed by the liberal activist group MoveOn.org and the American Federation of State, County and Municipal Employees, features a young mother with a baby criticizing McCain's determination to keep troops in Iraq. It began airing Tuesday in Ohio, Wisconsin and Michigan, USA Today reported. Pro-Democrat labor union leaders told the newspaper they have assembled millions of dollars for so-called independent...