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David Lauter, Tribune News Service

Immigration will figure prominently in the 2024 presidential campaign, continuing its run as one of the nation’s longest-running and most divisive issues. Republicans plan to feature the troubles at the southern border as evidence for their argument that President Joe Biden is failing. Former President Donald Trump has amped up his already inflammatory anti-immigrant rhetoric, accusing migrants of “poisoning the blood” of Americans. He focused on the subject again in his speech after winning Monday night’s Iowa caucuses, saying that if he were elected he would enforce “a deportation level that we haven’t seen in this country in a long time ... since the Eisenhower administration.” Democrats find themselves on the back foot. Public support for immigration, which rose during the Trump years, has sunk since Biden took office, no doubt partly because of chaotic scenes at the border. While immigration issues unify Republicans, they divide Democrats.

The Times’ most recent UC Berkeley Institute of Governmental Studies poll of California voters provided clear evidence of the party’s divisions: Asked whether immigrants in the U.S. without authorization have created a burden for the country, Republican voters almost unanimously said they did. Democrats were divided, with about 1 in 5 saying the migrants created a “major burden,” 2 in 5 saying they created a “minor burden” and about one-third saying they were not a burden.

The result is a one-sided debate: Republicans have relentlessly been on the attack, and Democrats have taken a defensive crouch. For the last couple of months, the White House, for example, has been trying to make concessions to Republicans in hopes of reaching a compromise on border security. So far, the talks haven’t achieved their goal, but the debate has further soured relations between the president and his party’s left wing. As the debate has droned on, neither party has seriously tried to grapple with the biggest issue: Just how many immigrants does the US need?

For any country, immigration poses a trade-off. On the one hand, newcomers bring new ideas, new resources and welcome vitality. The poll of American immigrants that The Times did last year with KFF, formerly the Kaiser Family Foundation, vividly illustrated how immigrants today are the keepers of the flame when it comes to optimism about the future — once a hallmark of American society. But high levels of immigration can also bring social instability. Large numbers of unskilled immigrants can depress wages in certain parts of the economy, at least for a time. And new residents with new customs can generate a backlash, as the US has vividly seen in recent years. Striking the right balance is complicated, but it starts with grappling seriously with the question of what level of immigration would be optimal.

The answer: A lot more — at least if the US wants to slow the graying of its population and stave off long-term population decline, demographers say.

This decade probably will experience the smallest percentage population growth in U.S. history, said Brookings Institution demographic expert William Frey. That’s partially the result of the COVID-19 pandemic, which increased death rates and caused some couples to postpone having children. But even with the pandemic receding, the US is heading for very little growth in the years to come. That’s a huge change from the past. Since 1900, the US population mostly grew between 1% and 2% each year. The exceptions came during traumatic periods — the Spanish flu epidemic of 1918-1919, the Great Depression. Now, according to Census Bureau projections, the country is, at most, likely to have about 4% population growth over this entire decade. The rate will slow further after that.

Should you worry about that? Some people would say no. Among environmental activists, for example, some take the view that fewer Americans would be a good thing because our lifestyle uses more resources than in other countries. But there are other ways to reduce the American impact on the global environment — greater reliance on renewable energy, for example. And a US population decline imposes real, and heavy, costs. If you plan to retire, or care about the country’s military strength or its economy, an aging or declining population is definitely something to be concerned about. An older population with a shrinking number of workers makes paying for Social Security or other retirement programs much harder, for example, because there are fewer workers to support a growing number of retirees.