A divided Supreme Court late Tuesday declined the Biden administration's request to pause a district judge's order to immediately reinstate former President Donald Trump's "Remain in Mexico" policy. President Biden had ended the program, formally called the Migrant Protection Protocols, on his first day in office. The Biden administration said it will take steps to comply with the ruling while it challenges the district judge's order, and immigrant advocates warned of another looming humanitarian crisis.

But there are at least three reasons the judicial intervention in immigration policy won't have any immediate effect. 

First, Mexico is under no obligation to follow the U.S. Supreme Court's ruling, and the U.S. can't start returning non-Mexican asylum seekers across the border without Mexico's permission. None of the 71,000 asylum seekers returned to Mexico under Trump's policy were Mexican.

The Supreme Court told "the Biden administration that they have to make a good faith effort to restart this program," NPR Mexico City correspondent James Frederick explained Wednesday. "So in theory, they could ask Mexico to restart it. Mexico could say no. And the Biden administration can turn around to the Supreme Court and say, we made efforts, but it's not possible because of Mexico. So in theory, the policy could die right there."

Some analysts argue that, given Mexico's cooperation with Trump's hard-line policies, a hard no is unlikely. But the Biden administration also has broad discretion over how it carries out a court-revived policy. "It could reimplement it on a very small scale for families who meet certain criteria from very specific nationalities, or it could do something broader," Migration Policy Institute analyst Jessica Bolter tells The Associated Press.

The third reason there should be no immediate effect is the pandemic. "The Trump administration placed roughly 6,000 migrants into the program from April 2020 to January 2021," out of 71,000 total, AP reports. Starting in April 2020, the Trump administration began blocking migrants from seeking asylum inside the U.S. through the Centers for Disease Control and Prevention's invocation of Title 42. The CDC renewed Title 42 in early August.

The Biden administration "has emphasized that Title 42 is not an immigration authority, but a public health authority, and its continued use is dictated by the CDC's analysis of the public health situation," AP reports. The end result is that most migrants still have to remain in Mexico.