MEXICO CITY — When I was in Tijuana last month, a heavy rainstorm poured down on the Benito Juárez sports park, where more than 6,000 Central American migrants were crowded into tents, under tarps, or simply sleeping on the mud.

The rain mixed with sewage that was leaking from broken toilets, forming putrid puddles that seeped into the tents and prompted a vain scramble for dry spaces. I saw one young mother squatting in filthy water, trying to comfort her sick baby. The city government eventually closed the park because of the unsanitary conditions.

The men, women and children who have traveled north in a stream of caravans in recent months have grabbed attention because it is unusual for people to move through Mexico together in such large numbers. It’s even more unusual for them to have to seek temporary shelter in such awful conditions. There are refugee camps in many places in the world, but that one existed right next to the American border, where its occupants could literally see California, is disturbing.

I’m worried that such scenes will come to seem normal. The Trump administration’s announcement on Thursday that it will make some asylum seekers wait in Mexico while their court cases are resolved in the United States makes this very likely.