46 U.S.C. § 53705: Pledge of United States Government

(a) Full Faith and Credit.—The full faith and credit of the United States Government is pledged to the payment of a guarantee made under this chapter, for both principal and interest, including interest (as may be provided for in the guarantee) accruing between the date of default under a guaranteed obligation and the date of payment in full of the guarantee. (b) Incontestability.—A guarantee or commitment to guarantee made under this chapter is conclusive evidence of the eligibility of the obligation for the guarantee. The validity of a guarantee or commitment to guarantee made under this chapter is incontestable.