AFTER THE measures designed by the Trump administration to terrify, threaten and deter migrants from seeking refuge in the United States, President-elect Joe Biden faces a needle-threading challenge immediately on taking office. As he seeks to recalibrate immigration policy so that it is more compassionate, rational and aligned with America’s traditions and interests, he must also avoid triggering a new humanitarian crisis at the Mexican border featuring unauthorized Central Americans and Mexicans streaming north to escape the economic fallout of recent hurricanes and the pandemic.

Make no mistake. Despite Mr. Biden’s distaste for the cruelty and bigotry at the heart of President Trump’s immigration policies, it would be self-defeating for the new administration to take steps that would encourage, intentionally or not, a new surge of illegal border crossing. Any hope of building public support for a legislative overhaul of the immigration system, let alone bipartisan backing in Congress, would be blown to pieces by fresh images of pandemonium at the border.

The president-elect acknowledged that explicitly Tuesday when he walked back campaign promises to immediately undo Trump administration asylum policies. “It will get done and it will get done quickly,” he said — but not on Day One.

The risk is real and building. More than 140,000 undocumented migrants were apprehended at the southern border in October and November combined, the highest numbers for those months in almost a decade. And that was despite the Trump administration’s policy of turning back nearly all detainees without an asylum hearing, on the basis of an emergency public health edict. A pair of devastating hurricanes in Central America, coupled with the economic ravages wrought by the pandemic there as well as in Mexico, are now thought likely to drive new waves of migrants.

Mr. Biden has pledged to end the Trump administration’s “Remain in Mexico” policy, which has forced tens of thousands of asylum seekers into camps south of the border, where they await word on their efforts to enter the United States legally. Mr. Biden’s instinct is right — the camps are squalid, and migrants there are victimized by predators. Yet any sudden move to abolish the policy without an orderly system to replace it could be read as a green light that would invite more migrants than the U.S. bureaucracy can process. Nor is it reasonable to swiftly revoke the emergency public health order authorizing the summary expulsion of unauthorized migrants at the border, based on the pandemic’s threat. That’s the right call at a time when the coronavirus is spreading aggressively on both sides of the border and Americans are barred from traveling to Canada and much of Europe. There are legitimate concerns that loosening restrictions on the southern border could speed covid-19’s march.

A return to the pre-pandemic regime of catch-and-release could be at least partly avoided by a more rational approach to immigration courts as well as judges, who have been leaving the bench in record numbers in response to the Trump administration’s meddling. In addition, the Biden administration should focus a concerted U.S. aid program on alleviating the poverty and violence that impel Central American migrants to seek better lives elsewhere.

As for the border, a patient, systematic overhaul of procedures is the best course for the post-pandemic future.