Mr. Biden, however, has continued to use a pandemic emergency rule to rapidly turn away most migrants at the border. Even though an appeals court allowed the United States to resume expelling minors, Mr. Biden has elected to welcome them into the country, where they must be kept in custody until they can be released to sponsors.
For Ms. Harris, the diplomatic assignment is likely to be challenging. Previous efforts, including one led by Mr. Biden when he was vice president, were largely unsuccessful, as critics charged that corrupt leaders there had not effectively spent foreign aid money. In the years since, a majority of the families crossing the border have traveled from Central America, seeking economic opportunity, safety from gangs and reunions with family members already in the United States.
The effort by Ms. Harris to address the root causes of migration, which can take years, is also unlikely to quickly produce the swift action demanded by Republicans and some Democrats to reduce the overcrowding at the border. Representative Henry Cuellar, Democrat of Texas, released photographs this week showing dozens of young migrants lying on mats under foil blankets in crowded pods in a tent facility managed by the Border Patrol in Donna, Texas.
“The administration is struggling between the humane, softer approach as opposed to Trump and they have to calibrate and find that balance in enforcing the laws on the books and still projecting compassion,” Mr. Cuellar said after touring an overflow facility managed by the Department of Health and Human Services that was established to move children quickly from the border jails.
As of Monday, more than 4,800 children and teenagers were still stuck in detention cells intended to hold adults for short periods, including more than 3,300 held longer than the maximum 72 hours allowed under federal law, according to government documents obtained by The New York Times. On Tuesday, the number of minors in the border facilities increased to more than 4,960, according to data released on Wednesday by the Department of Homeland Security. The largest number of minors held this way under the Trump administration was about 2,600 in June 2019, according to current and former Customs and Border Protection officials.