CHICAGO (Reuters) - After suffering a string of defeats in 2012, U.S. union leaders have little to celebrate, or to look forward to, as they mark the Labor Day holiday on Monday.
Stung by losses in former strongholds such as Wisconsin and Indiana, organized labor has pledged to spend more than $100 million to help President Barack Obama win re-election over Republican nominee Mitt Romney and reverse the Republican Party sweep of state legislatures two years ago.
But as the United States pauses for a national holiday honoring the union movement, there is a growing sense that labor's ability to deliver politically is fading just as it faces what could be its most important election in 80 years.
Organized labor's inability to twist arms of Democratic allies such as California Governor Jerry Brown and New York Governor Andrew Cuomo in recent pension fights has observers questioning whether it can deliver Michigan, Wisconsin or Ohio -- all battleground states run by Republican governors -- to the Democrats this fall.
"This is a very difficult Labor Day for union leaders. All they can really do is talk about labor history -- what there was rather than what there is or what there will be," said Gary Chaison, professor of industrial relations at Clark University in Worcester, Massachusetts.
Among labor leaders and experts, the November 6 election is seen as the most important since 1932, when Franklin Roosevelt defeated President Herbert Hoover and pushed pro-labor reforms into law as part of his New Deal program.
The Republicans, who wrapped up their nominating convention on Thursday, produced a platform more hostile to organized labor than any they have put forward in modern history, said Richard Kahlenberg, senior fellow at the left-leaning Century Foundation.
The platform calls for a national "right-to-work" law, a business-friendly, anti-labor measure that would prohibit union contracts from requiring workers to pay dues or other fees to the union.
In the 27 states without right-to-work laws, employees in union-represented workplaces are required to pay dues and fees.
The Republican platform also drops language from previous party planks that endorsed workers' right to unionize and characterizes collective bargaining by public employees as a threat to state and local government finances.
"It's a declaration of war on labor," Kahlenberg said.
The Democratic convention, which starts on Tuesday, is sure to produce a more union-friendly platform. However, Obama's track record on labor issues has disappointed some unions and left a palpable enthusiasm gap among rank-and-file members.
The administration's "Race to the Top" education reforms, for instance, designed to boost student performance, are reviled by many unionized teachers because of the emphasis they place on standardized tests and charter schools.
"The Democrats have sold us out, and there's a real questioning of the role the Democrats can play going forward," said Betty Maloney, a retired school counselor from Newark, New Jersey, who protested an appearance by Vice President Joe Biden at a recent teachers' union conference in Detroit.
As a result, organized labor's focus on the election reflects more an opposition to what Romney and the Republicans might do than an endorsement of Obama's track record.
"To me, Mitt Romney represents the wholesale capitulation to the interests of big businesses that don't want any unions in this country," said Roberta Lynch, deputy director of Council 31 for the American Federation of State, County and Municipal Employees in Chicago.
The location of the Democratic convention, in Charlotte, North Carolina, also rankles some. North Carolina is a right-to-work state with the lowest union penetration of the 50 states, according to the U.S. Bureau of Labor Statistics.
That snub aside, unions view the vote as a referendum on the direction of the country and are pulling out all the stops for Obama, said Harley Shaiken, a University of California, Berkeley, professor and labor historian.
"What they fear with a Romney administration is broken backs," Shaiken said. "That focuses the mind."
Unions represent about 11.8 percent of U.S. workers, down from 28.3 percent in 1954 at the peak of the labor movement, and a series of high-profile defeats have left them reeling and revealed potentially troubling weaknesses.
In Wisconsin, a 16-month union campaign failed to unseat Republican Governor Scott Walker, who had pushed through sweeping curbs on collective bargaining by public employees that made him a champion of fiscal conservatives.
Walker supporters out-spent unions seven-to-one, according to the Wisconsin Democracy Campaign, which tracks money in state politics. More concerning for unions was that their vaunted ground game, the mobilization of thousands of workers for door-to-door appeals, failed spectacularly.
Also in 2012, Republicans passed a right-to-work law in Indiana, a first for an industrial heartland state.
Unions also faced an aggressive overhaul of public employee pension and retirement programs in more than a dozen states, often spearheaded by erstwhile allies.
The reforms have been popular with voters and arguably were necessary to address big deficits but represent de facto pay cuts for public workers.
Unions have aimed to stem the tide, sometimes facing opposition from Democrats as well as Republicans.
In Michigan, they have pushed a voter initiative -- opposed by Republicans -- to enshrine collective bargaining rights in the state constitution for all workers.
In Chicago, public school teachers have voted to strike the country's third-largest district for the first time in 25 years if they cannot reach agreement to end an escalating fight with Mayor Rahm Emanuel -- a Democrat and former top aide to Obama.
The presidential contest traditionally begins in earnest after Labor Day, and unions are planning for a final push. AFSCME alone has pledged to spend $100 million between now and November on get-out-the-vote efforts.
Experts say labor's return on that investment, however, is likely to be minimal.
"One candidate, Romney, is opposed to their objectives," Chaison said. "The other, Obama, is only a fair-weather friend who asks for support by saying, 'I'm better than the other guy. If he wins, it will be worse.' It's not much of a choice."
Editing by Ellen Wulfhorst and Eric Beech