The meat of the U.S.-Mexico deal announced Friday by President Donald Trump lies in its provision massively expanding the administration’s “Remain in Mexico” policy — formally called Migration Protection Protocols — which requires certain migrants at the southwest border to be sent back to Mexico while their immigration cases unfold in U.S. courts.

The agreement largely consists of “initiatives that were already underway, but in some cases they represent, at least on paper, a large scale-up of previous commitments,” said Andrew Selee, president of the Migration Policy Institute, a nonpartisan think tank. “That’s particularly true of MPP, which the Mexican government has tried to keep limited but now seems ripe for a rapid expansion — if logistical considerations or the courts don’t prevent it.”

[Trump announces deal with Mexico to avoid tariffs]

Experts say the program’s expansion is unlikely to curb migration, but it could expand the magnitude of suffering at the southern border by separating even more families, restricting due process rights, and putting a growing number of vulnerable people — pregnant women, LGBT populations, and children — in harm’s way.

“By the time the courts are going to rule, it’s going to be too late for too many people,” said Robyn Barnard, a staff attorney at Human Rights First.