As Biden Prepares to Take Office, a New Rush at the Border

After the brutal 2018 “zero-tolerance” policy that separated children from their parents, the Trump administration last year introduced the Migrant Protection Protocols, or “return to Mexico,” forcing some 67,000 asylum seekers to await their immigration hearings on the southern side of the border.

The policy stranded people in squalid, gang-controlled makeshift camps. But it had the intended outcome of significantly reducing flows and compelling thousands of migrants already at the border to turn around and go home.

Because the “return to Mexico” policy is not codified by regulation, it could be immediately rescinded by the president-elect.

But the optics of large numbers of migrants suddenly being waved into the United States, or detained in facilities at the border, would create a public-relations nightmare for the new administration and almost certainly draw fierce condemnation from both immigration restrictionists and pro-immigrant activists, for different reasons.

“The new administration is going to have to find a way to push back on unrestrained, unauthorized migration with humane enforcement while dealing with people seeking asylum in an expeditious way that recognizes their legitimate claims,” said Michael Chertoff, secretary of Homeland Security during the Bush administration.

“It’s not going to be 10 minutes after inauguration, everybody come on in,” said Mr. Chertoff.

Any misstep would threaten a replay of 2014 and 2016, when the Obama administration scrambled to stem a chaotic influx of migrants from El Salvador, Guatemala and Honduras. Human-rights groups were outraged when families and children were locked up and deportations were accelerated. Immigration hard-liners attacked Mr. Obama for allowing tens of thousands to enter the United States and remain in the country while their asylum cases wound through the courts, which can take years.

And while Mr. Biden has said that he will cease construction of a wall, Mr. Trump’s signature project, there is no sign that his administration will refrain from deploying boots on the ground and sophisticated technology to capture border crossers.