WASHINGTON — Migrant children in the government’s care were placed in U.S. homes and left vulnerable to human trafficking due to sometimes non-existent screening by the Department of Health and Human Services, according to a congressional report released Thursday.

The investigation says HHS failed to run background checks on the adults in the sponsors’ households, failed to visit sponsors’ homes and failed to realize some sponsors were accumulating multiple unrelated children, which can be a sign of human trafficking.

Lawmakers contend the government weakened its child-protection policies as it was overwhelmed by tens of thousands of children crossing the border. A Senate subcommittee held a hearing Thursday to release the report and examine weaknesses in the department’s placement of migrant children.

At the hearing, HHS officials declined to fully answer many of the senators’ questions, at times saying they did not have the legal authority from Congress to follow up on the children.

Ohio Sen. Rob Portman, the chairman of the panel, says the HHS placement program for migrant children suffers from “serious, systemic defects.”