CHICAGO (Reuters) - U.S. labor unions, having helped Barack Obama win the presidency, entertain high hopes he will enact their agenda to bolster their negotiating power with employers and increase their numbers after decades of decline. Unions have "an unprecedented amount of leverage" after turning out white middle-class voters for Obama in battleground industrial states like Pennsylvania and Ohio that he won in Tuesday's election but had lost in the Democratic nominating primaries, said University of Illinois-Chicago labor expert Robert Bruno. "American workers won this election," said Anna Burger, chairman of the labor coalition "Change to Win" at a news...