They regrouped and continued their exodus north, escorted by the federal police and aided with water and medicines by Mexican townspeople along the way. Other caravans are reported to be underway. Does this migratory and diplomatic crisis have a solution?

Maybe not, but there is at least an explanation for it, which lies in another question. Why, after all his huffing and puffing, did President Trump accept a watered-down version of a renegotiated North American Free Trade Agreement, known now as the United States-Mexico-Canada Agreement, or USMCA?

No one knows for sure, but after nearly 40 years of being intimately involved, as an academic and public official, with these situations, I can offer an informed guess: The United States gave up most of its trade demands in exchange for a confidential commitment by Mexico to do Washington’s dirty work against would-be immigrants and refugees. Of course, this is speculation, and the evidence is all circumstantial.