The bank is authorized and empowered to obtain from any department or agency of the United States of America or from any nongovernmental insurer any insurance or guaranty (to the extent now or hereafter available) as to, or of, or for, the payment or repayment of, interest or principal, or both, or any part thereof, on any bonds or notes issued by the bank, or on any municipal bonds of governmental units purchased or held by the bank, pursuant to the provisions of this chapter; and notwithstanding any other provisions of this chapter to enter into any agreement or contract whatsoever with respect to any such insurance or guaranty except to the extent that the same would in any way impair or interfere with the ability of the bank to perform and fulfill the terms of any agreement made with the holders of the bonds or notes of the bank.