As the nation focused on South Florida and the FBI’s search of President Trump’s Mar-a-Lago home late Monday, the Department of Homeland Security announced that it was formally ending the previous administration’s “remain in Mexico” policy for asylum-seekers at the southern border.

The shift in policy means that many migrants seeking asylum will no longer be required to wait in Mexico for their cases to be heard and will instead be released in the United States. The decision — affecting what is formally known as the Migrant Protection Protocols, but popularly known as “remain in Mexico” —  came after a federal judge lifted an injunction earlier Monday that prevented the administration from moving to end the policy.

“As Secretary Mayorkas has said, MPP has endemic flaws, imposes unjustifiable human costs, and pulls resources and personnel away from other priority efforts to secure our border,” the homeland security department said.

The decision is sure to ignite passions on both sides over the crisis at the U.S.-Mexico border, where record numbers of illegal migrants have been crossing this summer. Most of them have been immediately released by immigration authorities, which has prompted border-state Republican governors to begin busing some of them to cities on the East Coast. The mayors of those cities say they are unable to cope with the influx.  

President Trump initiated the remain in Mexico program in late 2018 and sent as many as 70,000 asylum-seekers back to Mexico to await resolution of their cases. President Biden ended the program immediately upon taking office, but was forced to backpedal after being sued by Republican officials in border states, who said the influx of unauthorized foreigners is overwhelming their states.

The lawsuit eventually reached the U.S. Supreme Court, which ruled in late June that the homeland security chief, Alejandro Mayorkas, had the authority to end the program despite the Republican objections. The secretary was unable to do so, however, until the judge formally lifted his injunction.

Mr. Biden’s homeland security department has used the protocols much more sparingly than Mr. Trump’s did, enrolling a total of only 9,653 applicants between December 2021 and the end of June. During the same period, nearly 5,800 non-citizens were sent back across the border to wait out their cases.

Monday’s decision means that the asylum-seekers will be able to live in the United States until their cases are resolved, a process that can drag out for years because of the overburdened immigration court system.

The sparring between border state governors and East Coast mayors over the fate of thousands of migrants continued unabated on Tuesday. After slamming Governor Abbott’s practice of chartering buses to send the migrants to New York City as “horrific” and decrying the “use of innocent people as political pawns to manufacture a crisis” on Monday, Mayor Adams of New York City quipped Tuesday that he was calling his friends in Texas to get them to vote against Mr. Abbott in November’s elections.

“I am deeply contemplating taking a busload of New Yorkers to go to Texas and do some good old-fashioned door knocking,” Mr. Adams said. “For the good of America, we have to get him out of office.”

So far, Mr. Abbot has put several thousand migrants on northbound buses to Washington, D.C., and New York, both of which have demanded federal aid to help with the influx. The border patrol says some 200,000 migrants have been apprehended at the border during each of the last four months, the vast majority of whom are processed and then released into local communities in South Texas and elsewhere along the border.