The percentage of US workers in labor unions reached its peak in 1953, at more than a third of the workforce. Now, after decades of neoliberal assaults on the labor movement, only about 10 percent of US workers belong to unions. As the trend continues, unions struggle to retain political or economic relevance, unable to defend themselves against further efforts to undermine collective bargaining rights and workers’ living standards.

But all hope is not lost. As union density has declined precipitously in the private sector, it’s  held more of its ground in the public sector. And, as the number of private-sector strikes has dwindled over the decades, a strike wave emanating from the public sector took the nation by surprise last year.

The teachers’ strike wave was a windfall for the labor movement. And because public-sector unions have a special (which isn’t to say exclusive) ability to bargain for the common good — that is, to connect their demands to the well-being of the broader community — the teachers’ strikes likely contributed to the continuing rise in labor-union support among the general population. In 2018, Americans’ approval of labor unions reached 64 percent, nearly as high as when union density was at its peak.

But while public-sector unions have some unique capacities, so do private-sector unions, and we can’t build a strong and effective labor movement without them. While public-sector strikes can be effective by grinding essential services to a halt and creating political crises to which politicians and officials are forced to respond, private-sector unions have a grenade in their pocket. When private-sector workers go on strike, employers hemorrhage money. The six-week UAW strike this year cost General Motors nearly $2 billion.

Wages and benefits are not going to improve significantly in any part of the economy without significantly higher membership and renewed militancy in the private sector. The benefits of a stronger private-sector labor movement will accrue to public-sector employees, too, thanks to the greater political muscle the labor movement will gain. At the end of the day, every worker in the United States benefits from a stronger private-sector union movement.

That’s why it’s so heartening to see the Association of Flight Attendants–CWA (AFA-CWA) take on a big new organizing task: unionizing Delta flight attendants. Right now, the AFA represents flight attendants on twenty airlines — but not Delta. Delta is the white whale, the most profitable airline in the United States and the largest one whose flight attendants don’t have a union. If the AFA succeeds, it will absorb 25,000 new members — about half the AFA’s existing membership.

Unionizing Delta flight attendants won’t be easy. The company has successfully thwarted unionization efforts three times, in 2002, 2008, and 2010. But this time around, AFA president Sara Nelson thinks Delta may end up being a victim of its own growth: after merging with Northwest Airlines in 2008, the company integrated its flight attendants with former Northwest flight attendants in 2010. For nine years, many of the Delta crew members who voted no on forming a union have been working alongside Northwest crew members who do have a union.

The Northwest flight attendants have “been flying with the Delta flight attendants, [and] they’ve been able to talk to people about what that’s like,” said Nelson in an interview with Business Insider. “They know what it’s like to have a union contract, a voice at work, due process — all of those things.” Nelson suspects that more than a few minds have been changed.

“More than 40% of the flight attendant workforce has been newly hired since then,” Nelson notes. These new workers are coming from a population that is growing more approving of unions by the year. Americans are also starting to embrace more left-wing policies and anti-corporate candidates, a sign that they’re increasingly ready to put up a fight against corporations instead of passively regarding them as benevolent elites.

A positive outcome of the AFA’s unionization drive at Delta is not a foregone conclusion. But ambitious organizing projects like these are exactly what private-sector unions need to be doing — not just for the sake of workers in their own industries, but for all workers. Because they can tank profits and hit where it hurts, private-sector workers in strategic industries have enormous leverage. In fact, it was the AFA that helped stop Trump’s government shutdown earlier this year, threatening to strike if the government wasn’t reopened immediately. The president called off the shutdown just hours after Nelson gave the strike warning.

A labor movement that fails to organize big private-sector shops is leaving power on the table. By moving to unionize Delta, the AFA is showing it has no intention of doing that. As Nelson told members of the Democratic Socialists of America earlier this year, “People are ready to fight. People are waiting for answers and we have those answers for them. We need to open our arms to all working people and help them join us in building power — for all of us.”