via the Buck Stops here
The President has enhanced responsibility to resist unconstitutional provisions that encroach upon the constitutional powers of the Presidency. Where the President believes that an enactment unconstitutionally limits his powers, he has the authority to defend his office and decline to abide by it, unless he is convinced that the Court would disagree with his assessment. If the President does not challenge such provisions (i.e., by refusing to execute them), there often will be no occasion for judicial consideration of their constitutionality; a policy of consistent Presidential enforcement of statutes limiting his power thus would deny the Supreme Court the opportunity to review the limitations and thereby would allow for unconstitutional restrictions on the President's authority.
Some legislative encroachments on executive authority, however, will not be justiciable or are for other reasons unlikely to be resolved in court. If resolution in the courts is unlikely and the President cannot look to a judicial determination, he must shoulder the responsibility of protecting the constitutional role of the presidency. This is usually true, for example, of provisions limiting the President's authority as Commander in Chief. Where it is not possible to construe such provisions constitutionally, the President has the authority to act on his understanding of the Constitution.