Demonstrators rally in support of Wisconsin workers Feb. 26 at the Illinois State Capitol in Springfield, Ill. As other states move to weaken public employee bargaining rights in the aftermath of the Wisconsin showdown, unions and their allies dare to hope they can turn rage into revival. This could be a make-or-break moment for a movement that brought the nation the 40-hour week, overtime pay, upward mobility, and now a struggle to stay relevant in the modern age.

In this May 30, 1937, file photo, police using guns, clubs and tear gas wade into marching strikers outside Chicago’s Republic Steel plant during violent clashes in the early days of labor union organizations.

Washington ? Labor is roaring again, like in the old days. But it’s a wounded sound now.

In the bitter aftermath of a showdown with Wisconsin’s governor, and as other states move to weaken public employee bargaining rights, unions and their allies dare to hope they can turn rage into revival. This could be a make-or-break moment for a movement that brought the nation the 40-hour week, overtime pay, upward mobility, a storied century of brawls, progressivism and corruption — and now a struggle to stay relevant in the modern age.

Not so many answer to the call anymore when labor demands, as it did in the bloody strife of Kentucky coal country generations ago, “Which side are you on?”

One way or another, the Wisconsin Waterloo and the forces it set loose will fill a chapter in organized labor’s history. The dispute mobilized masses, attracted public support on the side of workers and set up a political donnybrook to play out in the months ahead as labor leaders seek voters’ vengeance against the Republicans who eviscerated union rights.

But it was, at the core, a defeat for labor in the one place where it has stayed strong: the public sector.

Suddenly this redoubt looks like a fat target.

“I think Republicans smell blood in the water,” said Leon Fink, a labor historian at the University of Illinois at Chicago. “Politics is a highly organized game of money ball and this could set back both the unions and Democratic Party power for years.”

Weakening unions

Since the heyday of organized labor’s influence in the 1950s, when union membership reached its peak at about one of every three workers, unions have fought a losing battle against the steady erosion of membership and clout.

Last year union membership fell to 11.9 percent of all workers, and just 6.9 percent of the private sector. The number of major strikes in 2009 and 2010 was the lowest on record.

If you’re a labor sympathizer wondering why unions got weak, pick your poison.

The decline of unions in the private sector mirrored the push to globalization, especially the loss of U.S. manufacturing jobs to other countries and the shift of other factories from the longtime industrial heartland to states less hospitable to organized labor.

Companies took an increasingly aggressive stance against union organizers, emboldened by the Reagan administration’s firing of 11,000 striking air traffic controllers in 1981. That act was taken as a wink to the corporate world that the long-established order was upended and that business, too, could play rough.

“Labor now gives off an almost animal sense of weakness,” Chicago union lawyer Thomas Geoghegan wrote in his Reagan-era ode to the movement — something of an obituary for it.

In the mid-1970s, when miners pulled off one of their multiple massive strikes, they choked coal production, idled steel plants that were starved of fuel and caused rolling brownouts in New York City. Americans far removed from strikes sharply felt their effects.

Not now.

In the 1970s, the nation saw an average of 269 major strikes or lockouts each year. The number has dropped precipitously ever since, to 17 per year over the past decade. The five in 2009 were the fewest since the Bureau of Labor Statistics started counting in 1947.

When industrial unions negotiated higher wages and better working conditions in more influential times, those advances rippled through the economy, setting a benchmark for union and nonunion workplaces. With less than 7 percent of the private sector unionized now, contracts no longer have the reach to raise all boats.

‘Sense of hopelessness’

Young workers today float from job to job and often have little vested interest in long-term improvements in employee satisfaction at a company. That has made it harder to organize new generations to replace the loyalists of old.

Nor are communities as cohesive as they once were.

When 1,900 miners staged an 11-month strike against Pittston Coal in 1989-90 to restore health and other benefits for retirees, widows and disabled miners, their makeshift Camp Solidarity drew thousands from across southwestern Virginia, West Virginia and Kentucky as well as from coal towns as far away as Canada. More than 37,000 participated in wildcat strikes throughout coal country to support the Pittston miners in a standoff that ranged between peaceful civil disobedience and ugly confrontation. The United Mine Workers finally won the day.

And now? It’s questionable how much common cause there will be between the public servants whose union rights are at risk and the rest of the population.

Instead of solidarity, says John Russo, labor studies professor at Youngstown State University, a “politics of resentment” may be in play.

“There’s a sense of hopelessness,” he says. “Some people feel like, ‘If we’re not going to go anywhere, I’m going to make sure nobody else is going anywhere.'”

To be sure, unions have made recent strides in pulling in new members in the service sector and health care industry. Labor remains a powerful political force. Senate Majority Leader Harry Reid, D-Nev., owes his narrow re-election victory last year to the dogged work of union organizers.

“There is no institution in America on either side of the aisle that has an infrastructure that gets people to the polls like the labor movement,” said Amy Dean, a former head of the AFL-CIO in California’s Silicon Valley. “Nobody can put people out on the streets and go door to door like we can.”