As President-elect Donald J. Trump’s second administration takes shape, his plans for a signature campaign promise are becoming clear: mass deportations of undocumented immigrants, including new detention centers, workplace raids and possibly the mobilization of the military to aid in expulsions.

Most economists are skeptical that this project will improve opportunities for working-class Americans. Mr. Trump and his allies don’t typically argue for purging undocumented immigrants on economic grounds; the case is more often about crimes committed by migrants, or simply a need to enforce the law.

But there is an intellectual movement behind immigration restriction that seeks to reshape the relationship between employers and their sources of labor. According to this rising conservative faction, most closely identified with Vice President-elect JD Vance, cutting off the supply of vulnerable foreigners will force employers to seek out U.S.-born workers.

“We cannot have an entire American business community that is giving up on American workers and then importing millions of illegal laborers,” Mr. Vance said in an interview with The New York Times in October, adding, “It’s one of the biggest reasons why we have millions of people who’ve dropped out of the labor force.”

Mr. Vance is correct that the share of men in their prime working years who are in the labor force — that is, either working or looking for work — has declined in recent decades, sliding during recessions and never totally recovering. (Women in that age group, 25 to 54 years old, are working at the highest levels on record.)

It seems like a simple equation: When fewer workers are available, employers have to try harder to compete for them. Certainly that dynamic played a role in the swift wage growth early in the pandemic, when people willing to do in-person jobs — waiters or nurses, for example — were in especially short supply.