The highlights from President Obama’s first State of the Union address of his second term. (The Washington Post)

Two kinds of middle-class Americans are struggling today — people who can’t find any work or enough work, and full-timers who can’t seem to get ahead.

Democrats and Republicans prescribe economic growth to help both groups. There was a time that would have been enough. But not today.

In the past three recoveries from recession, U.S. growth has not produced anywhere close to the job and income gains that previous generations of workers enjoyed. The wealthy have continued to do well. But a percentage point of increased growth today simply delivers fewer jobs across the economy and less money in the pockets of middle-class families than an identical point of growth produced in the 40 years after World War II.

That has been painfully apparent in the current recovery. Even as the Obama administration touts the return of economic growth, millions of Americans are not seeing an accompanying revival of better, higher-paying jobs.

The consequences of this breakdown are only now dawning on many economists and have not gained widespread attention among policymakers in Washington. Many lawmakers have yet to even acknowledge the problem. But repairing this link is arguably the most critical policy challenge for anyone who wants to lift the middle class.

Economists are not clear how the economy got to the point where growth drives far less job creation and broadly shared prosperity than it used to. Some theorize that a major factor was globalization, which enabled companies to lay off highly paid workers in the United States during recessions and replace them with lower-paid ones overseas during recoveries.

There is even less agreement on policy prescriptions. Some liberal economists argue that the government should take more-aggressive steps to redistribute wealth. Many economists believe more education will improve the skills of American workers, helping them obtain higher-paying jobs. And still others say the government should seek to reduce the cost of businesses to create new jobs.

The problem is relatively new. From 1948 through 1982, recessions and recoveries followed a tight pattern. Growth plunged in the downturn, then spiked quickly, often thanks to aggressive interest rate cuts by the Federal Reserve. When growth returned, so did job creation, and workers generally shared in the spoils of new economic output.

You can see those patterns in comparisons of job creation and growth rates across post-World War II recoveries. Starting in 1949 and continuing for more than 30 years, once the economy started to grow after a recession, major job creation usually followed within about a year.

At the height of those recoveries, every percentage point of economic growth typically spurred about six-tenths of a percentage point of job growth, when compared with the start of the recovery. You could call that number the “job intensity” of growth.

The pattern began to break down in the 1992 recovery, which began under President George H.W. Bush. It took about three years — instead of one — for job creation to ramp up, even when the economy was growing. Even then, the “job intensity” of that recovery barely topped 0.4 percent, or about two-thirds the normal rate.

The next two recoveries were even worse. Three and a half years into the recovery that began in 2001 under President George W. Bush, job intensity was stuck at less than 0.2 percent. The recovery under President Obama is now up to an intensity of 0.3 percent, or about half the historical average.

Middle-class income growth looks even worse for those recoveries. From 1992 to 1994, and again from 2002 to 2004, real median household incomes fell — even though the economy grew more than 6 percent, after adjustments for inflation, in both cases. From 2009 to 2011 the economy grew more than 4 percent, but real median incomes grew by 0.5 percent.

In contrast, from 1982 to 1984, the economy grew by nearly 11 percent and real median incomes grew by 5 percent.

Today, nearly four years after the Great Recession, 12 million Americans are actively looking for work but can’t find a job; 11 million others are stuck working part time when they would like to be full time, or they would like to work but are too discouraged to job-hunt. Meanwhile, workers’ median wages were lower at the end of 2012, after adjustments for inflation, than they were at the end of 2003. Real household income was lower in 2011 than it was in 1989.

Obama alluded to the breakdown between growth and middle-class wages and jobs in his State of the Union address. “Every day,” he said, “we should ask ourselves three questions as a nation: How do we attract more jobs to our shores? How do we equip our people with the skills needed to do those jobs? And how do we make sure that hard work leads to a decent living?”

But outside of some targeted help for manufacturing jobs and some new investments in skills training, the proposals Obama offered focused comparatively little on repairing the relationship between growth and jobs, or growth and income. Obama’s boldest plans included increasing the minimum wage and guaranteeing every child a preschool education. Both aim largely at boosting poorer Americans and helping their children gain a better shot at landing the higher-paying jobs.

The Republican response to Obama’s speech did not appear to nod to the new reality at all. Sen. Marco Rubio (Fla.) said that “economic growth is the best way to help the middle class” and offered few job-creation proposals that appeared materially different from what Republican politicians have pushed since the 1980s.

Economists are still trying to sort out what broke the historical links between growth and jobs/incomes.

Federal Reserve Bank of New York economists Erica Groshen and Simon Potter concluded in a 2003 paper that the recoveries from the 1990 and 2001 recessions were largely “jobless” because employers had fundamentally changed how they responded to recessions. In the past, firms laid off workers during downturns but called them back when the economy picked up again. Now, they are using recessions as a trigger to lay off less-productive workers, never to hire them back.

Economists at the liberal Economic Policy Institute trace the problem to a series of policy choices that, they say, have eroded workers’ ability to secure rising incomes. Those choices include industry deregulation and the opening of global markets on unfavorable terms for U.S. workers.

In the latest edition of their book “The State of Working America,” EPI economists argue that an “increasingly well-paid financial sector and policies regarding executive compensation fueled wage growth at the top and the rise of the top 1 percent’s incomes” at the expense of average workers.

Robert Shapiro, an economist who advised Bill Clinton on the campaign trail and in the White House, traces the change to increased global competition.

“It makes it hard for firms to pass along their cost increases — for health care, energy and so on — in higher prices,” he said. “So instead they cut other costs, starting with jobs and wages.”

Shapiro said the best way to restart job creation is to help businesses cut the costs of hiring, including by reducing the employer side of the payroll tax and pushing more aggressive efforts to hold down health-care cost increases.

Obama seems to have embraced an approach pushed by Harvard University economists Claudia Goldin and Lawrence Katz: helping more Americans graduate from college and go on to high-skilled, higher-paying jobs. It’s a longer-term bet. But as senior administration officials like to say, the problem didn’t start overnight, and it’s not likely to be solved overnight, either.