The U.S. population isn't growing as fast as it used to, and that’s a serious problem for economic growth, social stability and political sanity. Too bad the Trump administration won’t embrace the easy answer: more immigrants.

The latest plan from the administration, which the White House shared with several Republican senators Tuesday, reportedly aims to keep immigration levels stable — when waning population growth actually cries out for steps to boost immigration.

How drastic is the slowdown in population growth? Just last week, news emerged that California had experienced the slowest population increase on record. And the broader U.S. story isn’t much better. Yes, the nation’s population is still rising, but 2018 saw the smallest percentage increase since 1937.

The net effect of our slow-growing population is a dimmer economic and political outlook for Americans of all vintages, including working-class voters.

There are basically three reasons for this slowdown in population growth: Women are having fewer children; Americans are dying in greater numbers as the super-size generation of baby boomers start to cross that threshold; and we aren't making up the difference via immigration. In fact, the number of new immigrants has flagged during Donald Trump’s presidency.

The net effect of our slow-growing population is a dimmer economic and political outlook for Americans of all vintages, including working-class voters who may cheer the president’s varied efforts to reduce illegal border crossings and curtail legal immigration as a return to an earlier era of U.S. glory but in fact might be trapping themselves in a less prosperous future.

Among other things, lower immigration rates will hurt Social Security. Without new immigrants, America's low birth rate basically ensures that there will be fewer and fewer young people paying into the Social Security system — leaving it short of the cash needed to pay out promised benefits to older generations awaiting their checks.

Immigration can help fill in the gap. Just ask the trustees of the Social Security Administration. Their models show that higher immigration will improve the long-term viability of the program. Partly, that’s because legal immigrants tend to be younger, which means they'll pay into the Social Security systems for years — or decades — before they ever claim benefits.

In addition, there are several million unauthorized immigrants who pay federal taxes every year — including payroll taxes for Social Security and Medicare — despite the fact that they are not eligible to ever receive these benefits. And while taking money from unauthorized immigrants who will never enjoy the government benefit they’re funding may be troubling from a tax fairness perspective, there’s no denying the positive impact on Social Security’s accounting.

This is just one example of how increased immigration could help compensate for the problems of America's slow-growing population.

Consider that an ebbing population also means a slow-growing workforce. In fact, the only reason the working age population is expected to grow at all is because of new immigrants, according to projections from the Pew Research Center. Otherwise, the total number of 25- to 64-year-olds in the United States in 2035 will be 18 million lower than the number in 2015. That shortfall means the remaining workers will either have to work harder, longer or more productively simply to prevent the economy from shrinking.

Now it’s true there may be some other, nonimmigration-related fixes to this problem, including automation. Japan is often cited as a country that has embraced automation in response to workforce winnowing. And perhaps the workforce of the future won’t need to be so large, if machines take over more and more jobs — including the kinds of low-skill jobs often performed by immigrants. But it’s important not to be too halcyon here. Despite all the talk of AI and innovation, these technologies haven’t yet made companies more efficient or allowed them to dramatically produce more goods with fewer workers.

Ultimately, the deepest risk is that diminishing population growth seems bound up with the rise of populism. A definitive explanation hasn’t been found, but around the world you find a pervasive link between stagnating populations and populist parties. This is particularly true in rural areas that are seeing not just slower population growth but outright decline. Across the country, about half of rural counties have fewer residents than they did in 2000.

Calling for increased immigration in this climate of rising populism can seem quixotic. Especially given how entangled nostalgia and anti-immigrant sentiment seem to be in Trump's version of populism — where a “Make America Great Again” platform enables statements like the one Trump made at the border last month: "Our country is full."

But without immigrants, the social and economic challenges of a slow-growing population will only get worse. Particularly as the other solutions on offer — sharply increasing innovation or getting women to have a lot more children — are not readily achievable via legislation.

Ultimately, the deepest risk is that diminishing population growth seems bound up with the rise of populism.

This doesn’t have to mean open borders. In fact, it might be possible to take the Trump administration’s tightened control over the nation’s borders and use that to build an immigration system that is at once more generous and more targeted — allowing for many more entrants accompanied by more oversight of their level of education, skills, geographic destination, etc. Opening more paths to highly skilled immigrants already has some bipartisan support, as they tend to contribute more in taxes and economic value.

Then again, the U.S. was already attracting more highly skilled immigrants without any new laws. Since 1980, the share of U.S. immigrants with at least a bachelor's degree rose from 16 percent to 30 percent.

So maybe we don't need more controls. Just more immigrant workers to start businesses and immigrant taxpayers to support government programs like Social Security. That way we can keep the U.S. population growing and ensure that the U.S. economy remains vibrant.