When the question is so posed, we think that the answer is obvious. There is no doubt that the United States serves in a fiduciary capacity with respect to these Indians and that, as such, it is duty bound to exercise great care in administering its trust. See, e. g., Seminole Nation v. United States, 316 U.S. 286, 296-297 (1942). But it has long been recognized that a trustee is not an insurer of trust property. As Professor Scott has written, “A trustee is under a duty in administering the trust to exercise such care and skill as a man of ordinary prudence would exercise in dealing with his own property.” 2 A. Scott, Trusts 1408 (3d ed. 1967) (hereinafter cited as Scott). See, e. g., Phelps v. Harris, 101 U.S. 370, 383 (1880). It follows that “if the trust property is lost or destroyed or diminished in value, the trustee is not subject to a surcharge unless he failed to exercise the required care and skill.” 2 Scott 1419.
Applying these familiar principles to the facts before us, we are required to decide whether the United States can be said to have acted with less than the requisite care in refusing to contest the Oklahoma tax. When the State asserts a doubtful tax claim against trust property, the trustee is often presented with a close question. Normally, the trustee is obligated to pay taxes on the trust estate, and, indeed, if he negligently fails to do so, he may be held liable for any resulting penalty. See, e. g., 2 Scott 1422. Yet, as these cases demonstrate, if he pays the tax, he may similarly be called upon to reimburse the trust estate for the amount of the tax.