https://www.whitehouse.gov/presidential-actions/2025/06/department-of-defense-security-for-the-protection-of-department-of-homeland-security-functions/

In addition, the Secretary of Defense may employ any other members of the regular Armed Forces as necessary to augment and support the protection of Federal functions and property in any number determined appropriate in his discretion.

For private businesses sure, but Newsom has the authority to set up an escrow account and direct all state government entities to send their federal payroll taxes to the new account rather than to the IRS.