Can the United States come up with an immigration policy that will prove sustainable? Two writers whom I respect and take delight in reading, despite their widely differing views, Tyler Cowen, who favors more immigration, and Christopher Caldwell, who favors less, have their doubts. Both, incidentally, are writing for The Free Press.

They are writing at a time when President Donald Trump’s executive branch is splashily and aggressively enforcing supposedly unenforceable immigration laws, and Congress still has Trumpish Republican majorities.

Illegal immigration has been reduced toward zero, and the political stars seem in alignment, at least theoretically, for reductions in legal immigration as well.

But that seems unlikely. And not just because of timidity of lawmakers but because the two writers take too mechanical a view of mass immigration.

In my 2013 book, “Shaping Our Nation: How Surges of Migration Transformed America and Its Politics,” I argued that the unusual phenomenon of mass migration occurs when large numbers of people are pursuing dreams or escaping nightmares.

Cowen, a market-friendly economist, sees it differently. Looking back, he thinks that America had “a fine policy” before 2016, “keep(ing) borders nominally restricted … but allow(ing) immigration, both legal and illegal, to become increasingly attractive to people around the world.”

To which voters, as he points out, react negatively as they do to mention of an explicit open-borders policy.

The 1965 Immigration and Nationality Act imposed limits, for the first time, on immigration from Latin America, and few Mexicans arrived in the stagflationary 1970s. But mass chain migration to Ronald Reagan’s sunny California began in the 1980s and crested in the 2000s.

That led to the 2007 housing market collapse, which turned immigrants’ dreams of unloading their houses for $600,000 into bankruptcy nightmares. Net migration from Mexico turned negative for a decade, and the Biden-era surge of illegal immigrants came not so much from Mexicans but from Central Americans and assorted others, crossing Mexico to be welcomed across the Rio Grande. The Trump administration’s success in border and internal enforcement will, for a time, disincentivize illegal migration by turning would-be migrants’ dreams into nightmares.

While Cowen thinks that’s cruel, Caldwell hails it as a step toward “America’s third great slamming of the Golden Door.” The first, he dates from 1775 to 1815. The second started with passage of the Immigration Act of 1924, which virtually eliminated immigration from eastern and southern Europe, dominant in the Ellis Island era (1892-1914, 1919-24.)

The 1924 law remained in effect until 1965 and limited postwar immigration from Italy and Greece, but many prewar immigrants from those countries returned home.

Caldwell credits the “pause” in immigration following 1924 for encouraging assimilation into an American mainstream. But that was furthered more by the sudden appearance of mass media — radio, movies, television — and by World War II, which put 16 million men in a nation of 131 million into the military, putting literally in uniform Americans of all origins.

They partook of a common popular culture transmitted by universal media and established a national consensus that dismantled the separate segregation system established and maintained in the South for 75 years.

In the meantime, it’s an exaggeration to say that America is closing its doors when it swears in about 800,000 new American citizens every year. There are arguments for changing our legal immigration system to prioritize high-skill migrants, as well as to reduce or increase the total flow of immigrants. But there are limits on what the law can do when, despite incentives, people only take the unusual step of uprooting themselves to pursue dreams or escape nightmares.