Less than a week ago, President Trump issued a stern warning to the government of Mexico. They would need to step up their efforts to halt these caravans of migrants surging toward the United States or we would need to take steps that could impact both domestic policy on the southern border and endanger trade negotiations with that country. Do you think President Andrés Manuel López Obrador (AMLO) was paying attention?

The news from the southern portion of Mexico last night would indicate that he received the message loud and clear. A new migrant caravan had been making their way north, but instead of being welcomed with applications for asylum, hundreds were arrested by federal police and detained to await deportation. (Associated Press)

Central American migrants hoping to reach the U.S. now carry the added anxiety of the pursued after Mexican police and immigration agents detained hundreds in a surprise raid on a caravan in Mexico’s south.

While their compatriots were been taken into custody Monday, hundreds of other migrants scrambled away into the brush along the highway in Chiapas state to elude authorities.

Many had already learned they would not be received in towns with the same hospitality that greeted previous caravans, and now they know they won’t be safe walking along the rural highway either. Mexican authorities detained hundreds in the largest single raid on a migrant caravan since the groups started moving through the country last year.

AP journalists who have been traveling with the caravan estimate that as many as 500 arrests were made. The migrants were loaded into buses and taken to detention centers. Officials were going to interview them but expected the majority to be scheduled for deportation back to their home countries.

It’s true that the caravan had originally been estimated to contain up to 3,000 people, but this shrank the number considerably. A couple more raids like this could cut it in half. But this police action has the potential to move the needle in an important way. Up until now, these well-organized caravans have relied on two things. One is the strength that comes with numbers in terms of fending off the gangs that might otherwise prey on them. The other was the assumption that the Mexican authorities were going to mostly ignore them, if not assist them, and allow them to make their way to the U.S. border. If word gets around that this is no longer the case, the incentive to form up these caravans may begin to diminish.

AMLO is no dummy. He’s going to be dealing with Donald Trump for quite a while to come. There are trade negotiations to be worked out and questions of foreign aid. Much better to have a partner on the other side of the border than an opponent. And his own people, particularly near his northern border, have become increasingly distressed over the armies of migrants milling about. Mexico may have been reluctant to join us in these efforts at first, but it appears they now realize that it’s an investment for the future that they really needed to make.