An inflatable rat, or union rat, is often used by striking workers.Timothy A. Clary / Getty

On Tuesday night, as it became clear that voters in Missouri had—by a two-to-one margin—rejected a state law meant to reduce unions’ power, the president of the AFL-CIO, Richard Trumka, declared, “The defeat of this poisonous anti-worker legislation is a victory for all workers across the country.” He added, “Tonight is the latest act of working people changing a rigged system that for decades has been favoring corporations, the mega-wealthy, and the privileged few.”

The legislation in question was a law passed by the Republican-controlled state legislature last year and signed by the governor at the time, Eric Greitens, a Republican, which would have allowed employees in unionized private workplaces to opt out of belonging to a union and paying dues. Currently, unions in Missouri, as part of collective-bargaining agreements with employers, can require that an entire workplace be unionized. In those workplaces, even if someone isn’t keen to join the union, taking the job requires him to do so.

Missouri Republicans had hoped to bar that requirement, as 27 states have. Unions fiercely oppose such laws, partly on principle and partly because the laws represent an existential threat: Research has shown that when states have imposed such laws, known among supporters as right-to-work laws, union membership declines. So in Missouri, labor organizers collected enough signatures to put a measure on the state ballot, Proposition A, in order to put the issue to a vote. Then, according to The Wall Street Journal, they outraised their opponents five to one.

In positioning the vote as a milestone, Trumka is surely being self-serving, but he is hardly alone. The defeat of Proposition A is a defensive move—meant to maintain the status quo rather than actually make it any easier for workers to unionize. Still, it carried symbolic weight. Pointing to last spring’s walkouts by teachers in West Virginia, Oklahoma, and elsewhere, many commentators and politicians described Missouri’s vote as the most recent positive sign for the U.S. labor movement’s future. On Wednesday, The New York Times editorial board wrote, “Tuesday’s vote and the popular support for teacher strikes in red states show that unions have the wind at their backs for the first time in a long while.” On Rolling Stone’s website, Bob Moser said, “Workers across the country now have a model for going on the offensive against the rising plutocracy, rather than watching helplessly while wages continue to stagnate and inequality continues to widen.”

Those who are optimistic about unions’ future have some evidence supporting their views besides Tuesday’s vote. For one thing, political support for unions is rising in the United States. Gallup found last summer that 60 percent of people approved of labor unions, the highest level of support in 10 years. (Gallup hasn’t published figures for this summer.) In a poll conducted amid all the teacher strikes last spring, 52 percent of respondents said they approved of teachers leaving the classroom to strike for higher wages.

And yet, it’s not clear that popular support for unions, and for policies that help them retain members, is the right measure of their strength. Gallup’s poll last summer made headlines, but, with a couple of exceptions, public support of unions has been more or less constant: For several decades, as far back as the early 1970s, about 60 percent of people have said they approve of unions. And yet union membership has consistently declined in the United States: Last year, membership stood at the historic low of 11 percent, cut nearly in half from where it was in 1983, when the Bureau of Labor Statistics began tracking it. In the 1950s, according to separate data, more than one-third of workers were unionized. So while popular support for labor might seem to be a proxy for unions’ strength, it’s actually a bit beside the point.

The most consistent factor in determining union support seems to be the strength of the economy. Perhaps counterintuitively, support for unions and corporations follow similar trends, rising when times are good, and falling when they’re bad. When people have a job, they feel good about those that helped them get it—their unions, but also their companies. When they’re unemployed, their loyalty flags.

To understand what, besides public opinion, could really lead to a revival in union membership, it’s instructive to look at what was behind the decline. The Taft-Hartley Act of 1947, which severely restricted unions’ activities and allowed for the passage of state right-to-work laws, played an important role. Perhaps more significant though, especially recently, has been the rise of a globalized and automated economy. Those forces have decimated middle-class jobs in manufacturing and other traditionally unionized industries. They have also contributed to lower prices for U.S. consumers, which, in turn, has created jobs in industries that are built around selling stuff. The retail sector is now one of the biggest employers in the United States; it pays very little, and its jobs tend to be part-time and temporary—which discourages unionization, since employees would rather not pay dues for a job they don’t expect to hold for long.

All of this didn’t just happen. It has been helped along by decades of economic and business policies implemented by governments led by both Democrats and Republicans. Donald Trump’s trade protectionism and disdain for some Silicon Valley companies notwithstanding, it’s hard to imagine a reversal in the trends toward globalization and automation. If Trumka and his colleagues would like to position their recent success against the right-to-work movement as a proxy for union strength, and in turn for people’s ability to repair a rigged system, he may have underestimated the extent of the rigging.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.