With private-sector unions badly weakened by factory shutdowns and corporate resistance to unions, government employee unions have become the most powerful part of the labor movement. That’s one reason anti-union billionaires and foundations underwrote the Janus litigation: to hobble the strongest part of labor. The Koch brothers and other billionaires have seized on Janus to finance efforts, through emails and door-to-door canvassing, to urge government workers — teachers, police, firefighters, social workers and many others — to quit their unions and stop paying union fees.

It doesn’t look as if Mr. Trump’s latest nominee to the Supreme Court, Brett Kavanaugh, will be a friend to workers or unions. In an astonishingly anti-worker opinion in a case involving a SeaWorld trainer killed by an orca whale, Mr. Kavanaugh wrote in 2014 that the Labor Department was wrong to fine SeaWorld. Dissenting in a 2-to-1 case, he suggested that the Labor Department should not “paternalistically” regulate the safety of SeaWorld’s trainers because they, like tiger tamers and bull riders, were sports and entertainment figures who accepted the risk of injury in hazardous businesses that usually regulated their own dangers. His opinion had echoes of 19th-century state court rulings that factory workers assumed the risk of injuries from machinery that cut off their hands.

Labor unions might get a boost from Mr. Trump’s efforts to increase coal, steel and aluminum production and from his push to renegotiate Nafta to spur domestic auto production. The Trump administration and many unions hope those moves will bring back tens of thousands of mining and manufacturing jobs. That could lift unions’ ranks, but those gains would be a fraction of the losses expected from Janus. Some experts estimate that more than a million workers will quit their unions over the next few years as a result of that ruling.

There has been some good news for labor. A new Gallup Poll found that public approval for unions has reached its highest level in 15 years. Unions have scored some significant victories recently, especially among white collar workers: adjunct professors at many universities have unionized, and so have journalists at The Los Angeles Times, The Chicago Tribune, The New Yorker, HuffPost and Slate, and graduate teaching assistants at Harvard, Columbia, Brandeis and other universities. There have also been unionization gains among nurses and bus drivers as well as service-sector workers in Silicon Valley.

The labor movement in the United States is already far weaker than in any other major industrialized nation. Just one in 10 American workers belongs to a union, down from more than one in three in the 1950s. But in the face of decades of fierce employer resistance, compounded by the Trump administration’s hostility, unions are not making the gains they need to reverse their decline. If America’s unions don’t rebound, that will most likely mean even more income inequality and wage stagnation and even more control of the levers of power by corporations and wealthy donors.

Steven Greenhouse was a labor and workplace reporter for The New York Times for 19 years. He is writing a book about the history and future of the American labor movement.

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