Grant President Trump some bragging rights. After all, most economic news has recently favored Trump, including the 225,000 payroll jobs created in January. Naturally, he’s going to take credit if he can. Similarly blessed, a Democratic president would surely do the same. In his State of the Union address last week, Trump gushed self-congratulation. “Incomes are soaring, poverty is plummeting,” he said. “In just three short years, we have shattered the mentality of American decline.”

You need to take two cautionary messages from this — one short-term and one long-term.

First, the short-term: exaggeration.

Unsurprisingly, Trump’s appraisal contains much overstatement. Although incomes are rising, they are not “soaring.” The increases partly reflect catch-up from the Great Recession, when many households lost income to unemployment. In 2018, the median family income of $63,179 was only 3.6 percent higher than 2007’s $60,985. But it was 13 percent higher than the low point of $55,900 in 2012. The increases occurred under both the Obama and Trump presidencies.

The story is similar for poverty. In 2018, 11.8 percent of Americans fell below the government’s official poverty line (that’s $25,465 in income for a family of four with two children). That’s a big improvement from 2010’s 15.1 percent, but it’s virtually the same as 2001’s 11.7 percent. (All dollar figures have been adjusted to eliminate the effects of inflation.) Again, the improvement from 2010 was split between the Obama and Trump administrations.

Next, the long-term outlook.

Trump calls his policies “the great American comeback,” which — presumably — means faster economic growth and higher living standards. The realistic prospects are just the opposite: lower economic growth and smaller gains in living standards. Instead of the “great American comeback,” we’re facing the “great American slowdown.”

Let’s look at some numbers. In the 25 years after 1950, the U.S. economy grew about 4 percent a year, according to the Congressional Budget Office. Since then, growth has gradually decelerated. In recent projections, the CBO puts future growth at about 2 percent annually. This means there are fewer income gains to share among households, businesses and governments (federal, state and local).

The obvious implication is that we should raise the growth rate. Unfortunately, this is easier said than done. Economic growth stems from two basic sources: 1) growth in the labor force and the hours people work; 2) productivity, which is a catchall for efficiency (producing more for less). Changes in the labor force and productivity, added together, yield the economy’s overall growth rate.

Do the math. From 1950 to 1973, reports the CBO, the labor force and productivity grew at average annual rates of 1.6 percent and 2.4 percent, respectively, resulting in an overall growth rate of 4 percent. Now flash forward: For the next decade, the CBO projects 0.5 percent gains in the labor force and productivity gains of 1.4 percent. That’s almost 2 percent.

Government can’t easily alter these trends because they’re so big and all-encompassing. The slowdown in growth of the labor force reflects the retirement of the baby boom generation. That can’t be avoided. Productivity involves a multitude of forces: technology, workers’ skills, management, government laws and regulations, and more.

What kind of society does this create? Typically, lower economic growth is deplored because it squeezes private living standards and government programs. But in a fascinating new book (“Fully Grown: Why a Stagnant Economy Is a Sign of Success”), economist Dietrich Vollrath of the University of Houston challenges the conventional wisdom.

Past economic gains, he argues, have contributed enormously to popular well-being. For example: Women have more choices in how they lead their lives; mass retirement has become a reality for millions; there has been an explosion of personal services (health care, travel, eating out) made possible by the cheapness of goods.

But many of these gains have been exhausted. The explosion in schooling in the 20th century is a good example. There were millions of new high school and college graduates. But once this gain occurred, it couldn’t be easily repeated. It’s necessary to find new sources of growth or be content with low growth.

At the moment, we seem to be stuck in a perennially low-growth economy. Rather than complain, Vollrath says, we ought to celebrate it for what we have gotten in return.

This sounds sensible, but I doubt it would work in practice. Americans are an impatient people who are easily dissatisfied with the status quo. The future promises less cooperation and more contention, as groups and individuals fight over limited funds.

Whoever wins the White House in 2020 will have to confront this long-term mismatch. The rate of economic growth has subsided from its levels in the 1950s and 1960s, while popular demands for more private income and government spending have increased since the 1950s and 1960s. It’s not clear how or whether it will be resolved. What is clear, though, is that Trump and his many Democratic rivals are studiously ignoring the problem.

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