The low-wage jobs these laid-off workers found are more likely to come with variable schedules that make it difficult to arrange child care. Work hours have also stretched later and later, which hurts women more.

Even as women pushed their way into the workplace, the United States has done almost nothing to help make it easier for parents to work and raise a family at the same time. Unlike all other developed countries, the United States doesn’t guarantee parents any paid time off when they have children.

Francine Blau and Lawrence Kahn, economists at Cornell University, have found that while the United States had the sixth-highest female labor force participation rate in 1990, by 2010 it had fallen to 17th place. About a third of that drop, they say, could be explained by the fact that other developed countries instituted and expanded policies like paid family leave, subsidized child care and flexible work arrangements while the United States did barely anything at all.

It may very well be that the American women who were in the best position to make it all work — who faced the lowest hurdles to arranging child care and balancing work with family — have made it into the work force, but those who have bigger challenges simply can’t swing it. “A lot of women were able to make do, and those women are in the labor force,” Professor Blau said. “How do the rest come in without some kind of change?”

It’s unlikely that the country has simply hit a ceiling for how many women want jobs. If the United States were to spend more on helping parents get child care, ensure they can take paid time off work and protect those who want or need to work flexible schedules, it would almost certainly tap into this pool of women who have stepped away from work.

Helping them isn’t just something that is nice to do. If women keep getting pushed out, the economy will suffer. In 2012, one analysis found, the economy would have been 11 percent smaller if women’s labor force participation had remained at the levels of the late 1970s.

President Trump has said he wants to reach 3 percent G.D.P. growth. He would do well to focus on increasing how many women work. “He could probably get there much faster,” said Dr. Hartmann of the Institute for Women’s Policy Research, “if he tried to do more on equal pay and provided subsidized child care for everyone.”