The Biden administration is allowing asylum-seekers who have been living in limbo along the U.S.-Mexico border to enter the U.S. to await processing of their applications, a welcome redress of a cruelty inflicted by the Trump administration. But it also will force the new administration to confront a thorny situation that has bedeviled the U.S. government for years.

Under the new policy, up to 25,000 migrants in President Donald Trump's "Remain in Mexico" program — officially, the Migration Protection Protocols — will be allowed to enter the U.S. in small batches after they have been screened for the coronavirus. Then their cases will be transferred to courts near where they have relatives or places to stay.

Mindful of the message this might send, the administration has also warned those without pending asylum cases not to try to enter the country, though in truth some asylum-seekers have been gaining admission since Biden suspended new enrollments in the Remain in Mexico program.

This is where the problem is thorniest. Under U.S. law, anyone can show up at the border and request asylum. Those who asylum officers believe have demonstrated a credible fear of persecution if returned home are allowed to remain as their cases work through the immigration system. But the courts are hopelessly swamped with some 1.3 million pending cases, nearly double the caseload at the start of the Trump administration, and each case can take years to resolve.

Meanwhile, living conditions have deteriorated in Guatemala, Honduras and El Salvador — the home countries of most of the migrants reaching the U.S.-Mexico border — as back-to-back hurricanes ravaged regions that were already struggling with drought, limited job prospects and gang violence.

Although Biden has embraced a regional approach to try to ameliorate those "push" factors, chances of success are not clear. Meanwhile, migrants continue to move north.