By MONICA DAVEY

New York Times

MILWAUKEE >> Wisconsin Gov. Scott Walker’s foray into the Republican presidential field ended months ago, but he may yet have sway over the outcome.

Walker led a push five years ago to cut collective bargaining rights for most public sector workers, saying he needed to solve a state budget gap. Since then, union membership has dropped precipitously. Long a labor stronghold, the state has lost tens of thousands of union members, leaving Wisconsin with a smaller percentage of union members than the national average, new federal figures show.

The drop is most pronounced in the public sector: More than half of Wisconsin’s public workers were in unions before Walker’s cuts took effect. A little more than a quarter of them remain.

The shift has shaken the order of election-year politics. Democrats, who most often have been the beneficiaries of money and ground-level help from the unions, said they were uncertain about what the coming elections would look like, and what forces could take the place of depleted labor groups.

The change is certain to affect the Democratic presidential nominee in November. But Democratic political consultants are more concerned about the fate of state legislative contests, in which phone banks and extra door knocks have proved pivotal here in the past and which are seen as especially important if labor leaders hope to fend off the passage of more anti-union legislation.

“Maybe we can win high-profile races because Wisconsin still leans slightly Democratic, but at the level where Walker has produced the most profound change, it may prove very difficult to turn that around,” Paul Maslin, a longtime Democratic pollster in Madison, said. “That’s where we pay the price.”

Presidential races automatically draw large numbers of voters, often receive support from national labor groups and have seen the Democrat win Wisconsin every time since 1988. But other elections are looming, including an April contest for a seat on the sharply polarized Wisconsin Supreme Court and a highly anticipated fall rematch between Sen. Ron Johnson, a Republican, and Russ Feingold, his Democratic predecessor.

Top union leaders insist that labor remains a powerful election force.

“The people who have stayed have been much more politically active,” said Rick Badger, the executive director of the American Federation of State, County and Municipal Employees in Wisconsin, which last year condensed three thinning union locals into a single organization.

Phil Neuenfeldt, president of the Wisconsin State AFL-CIO, said, “We have been — and we will be — a big part of the election outcome.”

Yet declining membership, resources and money are creating an uncertain climate in which labor’s presence amounts, in the words of one Democratic strategist in the state, to “a stool with a missing leg.”

Walker was swept into the governor’s office as part of a national Republican wave in 2010, and both chambers of the state Legislature flipped to Republican at the same time. He immediately proposed broad changes to collective bargaining rights. Unions angrily objected, demanded a recall election and accused the governor of trying to crush them — a notion Walker has long denied.

“Governor Walker’s bold, common-sense reforms are about empowering taxpayers and putting them in control,” Laurel Patrick, his spokeswoman, said this month.

In addition to cutting collective bargaining rights for most public sector workers, Walker’s Act 10 generally required workers to contribute more for pensions and health plans. It forced unions to be “recertified” each year by a majority of those eligible to vote. And it ended so-called fair share requirements that public workers who opted out of union membership pay fees for the benefits of representation.

Last year, Walker signed legislation barring private companies from requiring such payments from those who opted out of unions. He recently signed an overhaul of the state civil service rules that will end some seniority protections and exams for job applicants.

The impact has been undeniable: Union numbers have fallen by more than a third by some estimates, with about 130,000 fewer members in the state. Some unions have dropped by more than half. Budgets have shrunk. Other union groups have failed recertification votes and vanished.

Some members said the waning influence of unions, combined with stalled wages and the rising costs of benefits, had forced them to make painful choices.

In Superior, in the state’s far north, 241 members remain in a union for which 361 public school teachers are eligible. Andrea Moreau, an instructional coach for other teachers, stopped paying monthly dues in November, saying higher pension and health care contributions were insurmountable obstacles for her, especially with two young children in day care and student loans to pay off.

“I stayed in the union a long time, and I feel really bad — like this is giving up in a lot of ways,” Moreau, 42, said.

Labor leaders say quieting the political voices of unions was always the intent of the changes in Wisconsin. Randi Weingarten, president of the American Federation of Teachers, described Walker’s moves as a “well-planned, diabolical and very efficient plan.”

Hillary Clinton, who hopes to be the Democratic presidential nominee and has relied on union support in the past, noted the decline of unions in a Democratic debate here. She accused governors like Walker of “trying to rip out the heart of the middle class by making it impossible to organize and stand up for better wages and working conditions.”

It is not just Wisconsin unions that have faced challenges. In Indiana and Michigan, Republicans have banned requirements that all employees at unionized workplaces pay union dues or fees.

In Illinois, Gov. Bruce Rauner, a Republican, is pressing for local versions of the “right-to-work” provisions, even as labor forces brace for a U.S. Supreme Court ruling in a case brought by California teachers who contend that forcing public workers to support unions they have declined to join violates the First Amendment.

Pockets of labor strength can still be found in the Midwest. Union membership rates grew some in Michigan and Illinois in 2015, according to federal estimates.

“Right now, as a whole, the labor movement is still strong in Illinois and is holding our ground,” said Roberta Lynch, an Illinois labor leader, “but there’s no doubt it’s a very perilous situation.”

Walker, whose approval ratings have fallen to 39 percent, has hinted at the possibility that he will seek a third term. But the governor’s race is not until 2018, and labor leaders see their best hope of blocking more restrictions in legislative races. In November, about half the seats in the Senate and all in the Assembly will be up.

Some political experts say the likelihood of shifting control of either chamber seems remote this year, though Martha Laning, chairwoman of the Wisconsin Democratic Party, said winning back the Senate was both possible and extremely important.

For now, some unions here are coping with shrinking numbers by changing their election-year tactics. At least 24 union members or retirees are candidates this year in local elections, mostly for school boards and county boards across the state. Some unions are working with broader, community-based groups; the Working Families Party, which helped fuel the rise of Mayor Bill de Blasio of New York, last summer announced a labor-backed Wisconsin branch.

Dave Eisner, an AFSCME leader here, has battled with Walker for decades, since the governor was the Milwaukee County executive.

“Do we have less boots on the ground? Yeah,” Eisner said. “Do we give the same amounts of money to the candidates? No.”

“But what people are now is fed up — they’re really mad,” he said. “So we’ve got that.”