in the case of a default in payment of the principal of any indenture security, when and as the same shall become due and payable, or in the case of a default in payment of the interest on any such security, when and as the same shall become due and payable and the continuance of such default for such period as may be prescribed in such indenture, to recover judgment, in its own name and as trustee of an express trust, against the obligor upon the indenture securities for the whole amount of such principal and interest remaining unpaid; and