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       A U.S. Border Patrol agent on horseback tries to stop a Haitian migrant from entering an encampment on the banks of the Rio Grande near the Acuna Del Rio International Bridge in Del Rio, Texas on Sept. 19, 2021.

       PAUL RATJE/AFP/Getty Images

       Dozens of migrants to the U.S., many of them Haitians, are fainting in the scorching Texas heat at a bridge where nearly 15,000 congregated over the past week. Women and children have grown ill, suffering from diarrhea and other viral ailments. And U.S. authorities are pledging to investigate after video circulated of border agents chasing migrants with horses.

       President Joe Biden came into office pledging a more humanitarian approach to the country’s borders.

       But the sudden arrival of large numbers of people to Del Rio, a small Texas border city, has cast the post-Trump U.S. in an ugly light, and provided new fodder for critics of Mr. Biden.

       “Failure to enforce laws that exist in the United States leads to chaos. And chaos leads to inhumanity,” Texas Gov. Greg Abbott said Tuesday.

       He spoke a short walk from the bridge across the Rio Grande, where 8,600 migrants remained, despite efforts by federal authorities to issue temporary papers to some — and place thousands of others on aircraft to be sent back to other countries, using a public health order that provides those migrants no chance to apply for asylum.

       The persistence of the camp, and the efforts to keep it from swelling further, have made it a particularly striking symbol of the harsh edges of U.S. policy toward migrants.

       “It’s essentially a refugee camp that’s been set up here,” said Nate Mook, the chief executive of Worldwide Kitchen, which has been brought in to feed migrants.

       “We have been seeing quite a bit of folks fainting, likely because of the heat,” he said. On Monday, temperatures in the sun exceeded 40 degrees Celsius. “It was so hot, dozens of people were passing out,” Mr. Mook said. Migrants have fashioned makeshift tents out of sugarcane and consumed water provided by federal agencies, which have rushed to feed those gathered by the bridge and provide medical treatment to those in need.

       Mr. Mook’s organization has been part of that response, buying up large volumes of food from local restaurants — much of it tacos — and providing diapers and baby food while they waited for the installation of kitchen equipment to provide other types of meals. That equipment should be in service by Wednesday, he said.

       “Everybody has been working non-stop in the heat,” he said, but “just getting that many meals out is a Herculean effort.” Elsewhere, medical tents have provided intravenous liquids to severely dehydrated migrants.

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       But those efforts have been overshadowed by the anger over other elements of the response to the arrival of so many migrants — in particular, the efforts to keep them out.

       Images of a Border Patrol chasing migrants — and grabbing one by the shirt — prompted widespread anger, including from Homeland Security Secretary Alejandro Mayorkas, who, after downplaying what took place, on Tuesday said he was “horrified” by what he had seen.

       In the images captured by multiple news organizations, a Border Patrol agent twirls a long cord in a whip-like fashion as he pivots his horse to block the advance of migrants out of the river waters. The video does not show the cord — which authorities called a long rein but right groups described as a lariat — striking migrants. But a photograph of the incident shows the agent, who is white, leaning out of his saddle with a menacing look as he grabs hold of the shirt of a migrant, who is black, barefoot and carrying several bags filled with Styrofoam boxes that appear to be used for food.

       “I thought the Haitians were quite scared,” photographer Paul Ratje told NPR, as his image became the focal point in the debate about how the U.S. treats those attempting to make an unauthorized entry into a country built by immigrants.

       Veronica Escobar, a Democratic Congressional Representative from Texas, called it “absolutely unacceptable,” writing on Twitter: “No matter how challenging the situation in Del Rio is right now, nothing justifies violence against migrants attempting to seek asylum in our country.”

       In another image captured by Mr. Ratje, a mounted Border Patrol agent bares his teeth as he advances toward a migrant stumbling backward into the water. A different video captured audio of an agent labelling a migrant’s country of origin with a derogatory epithet.

       U.S. Customs and Border Protection said its office would investigate, amid an uproar from the highest levels of the country’s administration.

       “What I saw depicted about those individuals on horseback treating human beings the way they were was horrible,” Vice-President Kamala Harris said Tuesday. “And I fully support what is happening right now, which is a thorough investigation into exactly what is going on there. But human beings should never be treated that way. And I’m deeply troubled about it.”

       Homeland Security Secretary Alejandro Mayorkas initially described what happened as normal practice, saying, “to ensure control of the horse, long reins are used.”

       The Border Patrol has used agents on horseback from its inception in 1924, and operating near a river is “a difficult situation,” Border Patrol Chief Raul Ortiz added at the time. “Trying to maintain control of those horses so we do not get in a position where we injure a migrant as they’re trying to make that treacherous trek across the river is probably more important than anything.”

       On Tuesday, however, with criticism building of how the migrants have been treated, Mr. Mayorkas issued a stronger condemnation. “Any mistreatment or abuse of a migrant is unacceptable,” he told CNN. “The pictures that I’ve observed troubled me profoundly.”

       Human rights groups, however, demanded more. The Texas chapter of the American Civil Liberties Union said the treatment of the migrants in the state echoed some of the ugliest chapters in the country’s history.

       “The agents’ conduct — and the agency’s immediate response to the situation — are in line with decades of systemic racism against Black immigrants,” the ACLU wrote in a public demand. It called for the agency to immediately remove horse-mounted units from the area, discipline agents and make explicit that “lariats, whips, or any other rope should not be used as weapons by agents under any circumstances.”

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