Liftoff & Letdown : The American middle class is floundering, and it has been for decades. The Post examines the mystery of what’s gone wrong and shows what the country must focus on to get the economy working for everyone again.

Green once held a middle-class job. Now, to make enough money to send his children to college, he works the equivalent of two full-time jobs: one maintaining highways for the state of North Carolina and one ushering fans and collecting trash for a variety of sports teams around Winston-Salem.

The American economy has stopped delivering the broadly shared prosperity that the nation grew accustomed to after World War II. The explanation for why that is begins with the millions of middle-class jobs that vanished over the past 25 years, and with what happened to the men and women who once held those jobs.

Millions of Americans are working harder than ever just to keep from falling behind; Green is one of them. Those workers have been devalued in the eyes of the economy, pushed into jobs that pay them much less than the ones they once had.

Today, a shrinking share of Americans are working middle-class jobs, and collectively, they earn less of the nation’s income than they used to. In 1981, according to the Pew Research Center, 59 percent of American adults were classified as “middle income” — which means their household income was between two-thirds and double the nation’s median income. By 2011, it was down to 51 percent. In that time, the “middle” group’s share of the national income pie fell from 60 percent to 45 percent.

For that, you can blame the past three recessions, which sparked a chain reaction of layoffs and lower pay.