The Senate’s failure to confirm labor lawyer Craig Becker to the National Labor Relations Board was just the latest blow, but the frustrations have been building for months.

"Here's labor getting thrown under the bus again," said John Gage, the national president of the American Federation of Government Employees, which represents 600,000 workers. "It's really frustrating for labor, and a lot of union people are thinking: We put out big time in money and volunteers and support. And it seems like the little things that could have been aren't being done."

The 52-33 vote on Becker — who needed 60 to be confirmed — really set labor unions on edge, but the list of setbacks is growing.

The so-called “card check” bill that would make it easier to unionize employees has gone nowhere. A pro-union Transportation Security Administration nominee quit before he even got a confirmation vote. And even though unions got a sweetheart deal to keep their health plans tax-free under the Senate health care bill, that bill has collapsed, leaving unions exposed again.

Union leaders warn that the Democrats' lackluster performance in power is sapping the morale of activists going into the midterm elections.

"Right now if we don’t get positive changes to the agenda, we’re going to have a hard time getting members out to work," said United Steelworkers International President Leo W. Gerard, in an interview.

“There’s no use pretending any longer.”

The biggest threat, of course, is apathy from a Democratic constituency that has a history of mobilizing for elections.

"You're just not going to be able to go to our membership in the November elections and say, 'Come on, let's do it again. Look at what the Democratic administration has done for us!'" Gage said. "People are going to say, 'Huh? What have the Democrats done for us?'"

Kim Freeman Brown, the executive director of a D.C.-based nonprofit called American Rights at Work, acknowledged "frustration" with the lack of movement.

"I implore Congress to listen to the voice of their constituents who want change, and so far we haven't delivered good enough on that promise," she said. "To the degree that we don't address these real bread-and-butter issues, we will have failed America's workers."

Gage warned that Democrats will struggle to energize blue-collar voters if they don't score a few victories soon. Union leaders say they will closely watch as a new "jobs bill" emerges to see if it includes more labor-friendly provisions or tax cuts for small businesses.

When you talk to labor officials these days, much of their animus is directed at Sen. Ben Nelson (D-Neb.), who helped filibuster Becker's confirmation.

"Ben Nelson has got principles until you buy him off," Gerard said.

A group affiliated with the Service Employees International Union, called Change That Works, had defended Nelson's support for an unpopular health care reform bill in his home state.

But the Nebraska director of that group, Jane Kleeb, now criticizes Nelson for not allowing the Becker nomination to come to the floor for an up-or-down vote. And Bill Samuel, legislative director for the AFL-CIO, accused Nelson of following a "double standard" since he had argued that the nominees of then-President George W. Bush should get up-or-down votes.

Another AFL-CIO spokesman, Eddie Vale, pinpointed Nelson, saying he had "let down" working families.

Nelson said Becker’s stance on labor issues made him worry whether he would be "impartial" in making NLRB decisions.

But labor unions can’t pin all their blame on Nelson. The failure of a wide range of union priorities has been deflating for the labor movement, which seemed destined to be one of the biggest beneficiaries of Barack Obama’s presidency.

And with unemployment hovering around 10 percent, special treatment for unions has only served to harm the movement.

On health care, unions found themselves in a defensive posture. They worked in early January to carve out an exception from an excise tax on so-called Cadillac insurance policies, only to see the package fall apart, with recriminations about just the kind of back-room deal making they had engaged in.