Mr. David Dudley Field, on behalf of Lamdin P. Milligan, argues, regarding the prerogative power of the president, that:

The oath of office cannot be considered as a grant of power.  Its effect is merely to superadd a religious sanction to what would otherwise be his official duty, and to bind his conscience against any attempt to usurp power or overthrow the Constitution (Ex parte Milligan, 71 U.S. 2 (1866)).