WaPo reported earlier that Trump's threats to close the border helped convince the incoming Mexican administration to accept the new policy.

With border crossings skyrocketing to the highest levels of the Trump presidency (they hit 60,000 last month) and federal judges once again stymieing the president's plans to crack down on border crossings, the Trump Administration has quietly negotiated an agreement with Mexico that effectively circumvents US courts to implement one of Trump's biggest immigration-policy wins so far: A plan that will keep Central American applicants for asylum in the US on the Mexican side of the border while their claims are processed.