42 USC 1320b-15 – Protection of social security and medicare trust funds

(a) In general

No officer or employee of the United States shall—

(1) delay the deposit of any amount into (or delay the credit of any amount to) any Federal fund or otherwise vary from the normal terms, procedures, or timing for making such deposits or credits,

(2) refrain from the investment in public debt obligations of amounts in any Federal fund, or

(3) redeem prior to maturity amounts in any Federal fund which are invested in public debt obligations for any purpose other than the payment of benefits or administrative expenses from such Federal fund.

(b) “Public debt obligation” defined

Terms Used In 42 USC 1320b-15

Obligation: An order placed, contract awarded, service received, or similar transaction during a given period that will require payments during the same or a future period.
officer: includes any person authorized by law to perform the duties of the office. See 1 USC 1
Public debt: Cumulative amounts borrowed by the Treasury Department or the Federal Financing Bank from the public or from another fund or account. The public debt does not include agency debt (amounts borrowed by other agencies of the Federal Government). The total public debt is subject to a statutory limit.
United States: means (but only for purposes of subparagraphs (A) and (B) of this paragraph) the fifty States and the District of Columbia. See 42 USC 1301

For purposes of this section, the term “public debt obligation” means any obligation subject to the public debt limit established under section 3101 of title 31.