Illegal immigration is a real problem, but Trump doesn’t have a serious solution.

The Senate last week failed to advance an immigration-reform bill, continuing a trend of futility stretching back decades. The last serious immigration-law overhaul was in 1986, during Ronald Reagan’s second term, and its failure to stem the tide of illegal immigration helped discredit future attempts. But the issue won’t go away, and the recent surge in illegal crossings at the southern border has moved the issue to the center of the 2024 presidential contest. A Wall Street Journal poll conducted in March found that, in seven swing states, immigration ranked as one of voters’ top two concerns. Americans are right to be worried, and it’s wrong to defend mass violations of U.S. law, but the unfortunate reality is that there’s no easy fix. One important aspect of immigration is its effect on demographics. For a population to replace itself, according to demographers, women must have an average of 2.1 children each. The U.S. has fallen below replacement rate in most years since the 1970s. The Centers for Disease Control and Prevention reported in April that the fertility rate in 2023 was 1.62, the lowest on record. The fertility rate is falling in other countries as well, both in advanced and in developing economies. A low fertility rate means fewer young adults entering the workforce to replace retirees, leading to labor shortages—unless immigration makes up the difference. In a recent analysis published in these pages, TrendMacro CEO Donald Luskin estimated that foreign-born people represent 80% of the adult-population increase in the U.S. since July 2022 and account for 71% of the 2.5 million new jobs. Without these workers, he estimated, the economy would have grown “less than a third as much as it actually has.” Many Americans fear that foreign-born workers will take jobs away from native-born workers, but immigrants often do the lower-paying, physically demanding, less desirable types of work that keep businesses afloat. “The work of the U.S. citizen serving a table in a restaurant is complemented by the work of a possibly unauthorized worker in the back of the restaurant,” Michael Clemens, an economist at George Mason University, told the Washington Post. “Neither of these jobs can happen without the other.” These economic considerations haven’t changed the minds of most Americans, who see firsthand the pressure that new immigrants put on housing markets, public schools and local public services. The immigration surge also has exacerbated fears about crime, even though a recent study from Northwestern University found that immigrants are less likely to be incarcerated than people born in the U.S.

Mr. Trump’s advisers and allies are working on the details of a plan to help him achieve his immigration objectives. The logistics are daunting, as are the legal and diplomatic obstacles. Polls show that while Americans are worried about the issue, they’re deeply split on whether they support immigrant arrests, deportations and detention camps.

More From The Wall Street Journal (subscription required):