Mr. Biden hopes to stem the flow of migrants before they arrive at the U.S. border and has turned to Mexico—just as the Trump and Obama administrations did before—to step up enforcement at its own southern border with Guatemala. Mr. Biden has also asked Vice President Kamala Harris to work with Mexico and the Northern Triangle countries to lead the administration’s diplomatic efforts.

Several senior White House officials including Roberta Jacobson, the administration’s border coordinator, traveled to Mexico and Guatemala this week to hold talks with the governments of those two countries.

Besides the diplomatic efforts, officials are trying to find more bed space for unaccompanied minors at shelters run by the Department of Health and Human Services, so they can be more quickly moved out of Border Patrol custody. On Wednesday, there were 4,962 unaccompanied children in Border Patrol custody, according to figures provided by the Department of Homeland Security. The administration also announced it was opening another emergency intake shelter, this time at the San Diego Convention Center, to house up to 1,400 minors…

With the numbers of unaccompanied minors climbing, Mr. Biden continues to face pressure from both Democrats and Republicans, especially those from border states. “The policy does need to change,” said Rep. Vicente Gonzalez (D., Texas), who represents a section of the border. “I’m concerned they don’t totally have this figured out.”