Treasury Secretary Scott Bessent gave Mr. Musk’s representatives at the so-called Department of Government Efficiency a powerful tool to monitor and potentially limit government spending.

A senior U.S. lawmaker says representatives of Elon Musk were granted “full access” to a U.S. Treasury payments system used to disperse trillions of dollars to Americans each year, and warned that Musk’s access to the system poses a “national security risk.”