President Trump evidently knows something about the art of the tariff threat. His unorthodox Twitter diplomacy has gotten Mexico to make potentially important public commitments on immigration enforcement.

Trump said he was going to slap steadily escalating tariffs on Mexico unless it did more to help with the border crisis, a threat with huge downside risks. If implemented, the tariffs would have been disruptive at a time when U.S. growth is perhaps slowing, been an economic gut-punch to an allied country whose stability is important to us, and probably precipitated a congressional revolt against the policy. Instead, Trump has a win that is likely more than a mere PR victory.

Mexico is devoting 6,000 troops to attempting to better police its own border with Guatemala. It’s unclear what this will produce, although it can’t hurt. More important is the extension of the Migration Protection Protocols (MPP), or the “remain in Mexico” policy. Under this arrangement, we can return asylum-seekers to Mexico while their claims — almost always ultimately rejected — are adjudicated. This avoids one of the biggest problems of our current policy, which allows asylum-seekers into the country, never to be removed, even if their claims are rejected and they are ordered deported.