Union membership grew rapidly during her tenure and continued to do so in the immediate post-World War II decades, reaching a peak in the mid-1960s, when at least a third of all wage-earners in the upper Midwest states belonged to unions. In Michigan — the quintessential manufacturing state — the share stood at 45 percent in 1964, or nearly half of that state’s work force. Simply by their numbers, unions had the leverage to slow manufacturers who wanted to build factories abroad.

By the late 1970s, however, the merchandise trade deficit — the excess of imported goods over exports — turned negative. (It grew to almost $800 billion last year.) The many benefits of global trade have come at a tremendous cost to American workers. As the trade deficit swelled, unions lost much of their power.

Think about it: A huge amount of what America consumes is made overseas, with the implicit consent of the nation’s now nearly neutered industrial unions. There were just seven strikes that involved at least 1,000 workers in 2017, according to Labor Department records. From 1968 to 1983, in sharp contrast, the total number of strikers across the country fell below 10 million in only one year — 1982. After that period, the annual total exceeded 10 million only three times.

In 1983, union membership was 17.7 million — representing 20 percent of all wage and salary workers. Last year, it was 14.8 million, representing just 10.7 percent of those workers. No wonder President Trump can talk about making America great again and not feel much pressure from organized labor to do much about it.

As union membership declines, labor has less leverage to intervene in the management of a corporation, or to galvanize the public into boycotting the products of manufacturers who put too many factories overseas while exporting less from the United States.

Strikes work when union membership is high enough to encourage the public to support the strikers, or at least feel a kinship with them. My parents, who lived comfortably on my father’s earnings as a textile broker in New York, never crossed a picket line thrown up by a labor union in pursuit of a favorable contract. They might not have agreed with a union’s demands, or even known what they were. But they respected a strike as an often-necessary tool in reaching a compromise acceptable to both sides.

They wanted that compromise. They had been young adults during the Depression, and they did not want to see, once again, the vagrancy and hunger that had been so commonplace — so visible — in the 1930s. That sentiment resurfaced for many Americans in 1965, when Cesar Chavez dug in his heels against California’s table grape growers, organizing a strike against them and calling — successfully — for a nationwide boycott of their grapes.