But the source of the president’s frustration was as much from inside his administration as it was from outside. As border crossings increased, disagreements erupted over how quickly to dismantle Mr. Trump’s anti-immigrant policies and what to replace them with…

Xavier Becerra, the secretary of health and human services, whose department runs shelters for migrant children, said the Department of Homeland Security needed to be more aggressive in turning away older teenagers, which would have changed Mr. Biden’s policy of letting all unaccompanied migrant children into the country. Ms. Rice repeatedly said Mr. Becerra should provide more shelters. Alejandro N. Mayorkas, the secretary of homeland security, said the Department of Health and Human Services needed to move the children more quickly out of overcrowded Border Patrol stations.

Mr. Klain tried to play mediator, to little effect.

For months, aides clashed over an effort intended to speed up consideration of asylum cases at the border by allowing immigration officers to decide the claims rather than overburdened judges. The goal was to streamline a court process that currently takes an average of five years to reach a decision for asylum seekers.