A major reason for the drop in apprehensions at the border this year: Mexico is stopping migrants well before they reach the border.

With detentions at the U.S. border plunging to a four-year low, everyone is angling for the credit. Democrats highlight President Joe Biden’s tougher asylum policies. Republicans point to Gov. Greg Abbott’s razor-wire barriers on the Texas border. But a major reason for the drop can be seen 800 miles south of the border in this sleepy, palm-shaded city closer to Guatemala than to the United States. Here, sleek white government buses roll in, one after another, to disgorge groups of bewildered migrants. The foreigners have been stopped at highway checkpoints or plucked from buses and trains, caught in a massive dragnet set up by Mexico under U.S. pressure. But the government can’t afford to deport them. So it sends them back here to southern Mexico — where many simply turn around and head north again. Officials call it “El Carrusel.” The merry-go-round.

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