PRESIDENT BIDEN has served notice that his ambitious immigration plan is in the first rank of his priorities. Some of his program will be immediately implementable; some may get bogged down in Congress, where many Republicans will regard it as an occasion to brandish the word “amnesty,” red meat for their bases. No matter. Mr. Biden’s plan is in keeping with the United States’ best traditions. It responds to the challenge of population stagnation. It would reverse his predecessor’s extravagantly cruel policies. And it is now clear that when it comes to immigration, Mr. Biden is all in.

That courageous stance was not necessarily expected or politically expedient. Unity was the new president’s campaign theme and inaugural touchstone, yet few issues are as divisive as immigration. His evident readiness to tap his modest reserves of political capital for a slugfest on immigration is a signal that the United States has returned to its roots as a beacon for refugees and a humanitarian role model among nations.

The plan is also smart. The U.S. population growth rate in the just-ended decade was the lowest since the first national census in 1790, according to the Brookings Institution — lower even than during the Great Depression of the 1930s. The number of Americans below the age of 18 actually shrank in the 2010s, by more than 1 million.

That stagnation, the product of an aging population and historically low fertility rates, cannot be reversed by immigration alone. But it will certainly be exacerbated, and has been in the past four years, by a policy hostile to newcomers. In President Donald Trump’s penultimate year in office, annual net immigration fell below 600,000, the lowest level in decades; it was more than 1 million in the final years of the Obama presidency.

What’s more, by proposing an eight-year path to citizenship for most of the nation’s 11 million unauthorized migrants — the centerpiece of his plan — Mr. Biden is attempting to align law and reality. By 2029, when they would be eligible for citizenship, most will have been in the United States for more than a quarter-century. At least 4 million are essential workers in construction, food processing, groceries, restaurants, agriculture and transportation — doing jobs critical to practically every American.

Mr. Biden is moving quickly where he can — fully reinstating the Obama-era program providing work permits and deportation protection for “dreamers,” young migrants brought to this country by their parents; rescinding Mr. Trump’s 2017 travel ban from majority-Muslim countries; halting construction of the southern border wall; and reining in the Trump administration’s aggressive deportation policies. He has also signaled he will increase annual refugee admissions, which Mr. Trump poleaxed, and scrap a Trump administration rule that denies green cards to immigrants deemed likely to use public benefits such as food stamps.

Other measures will require congressional action. Under legislation Mr. Biden is sending to Congress, green cards conferring legal permanent residency would be granted to dreamers as well as to immigrants from strife- and disaster-wracked nations who have been here for years.

The president is also pushing tougher border security — in recognition that the new administration is not inviting a wave of new migrants, still less amid a pandemic — though not as a precondition for his immigration reforms. His more impactful, long-term strategy to dissuade new waves of illegal immigrants is a concerted aid effort to boost economies and contain crime in Central America.

Mr. Biden has laid out an immigration program that would genuinely put America first.

Read more: