[inquest]

The War Powers Resolution of 1973 was vetoed by Nixon, but put into law by a Congressional supermajority. The Constitutionality of that law has not been put to the test, but at least Dick Cheney (and many others) hold that it represents an unconstitutional encroachment by Congress.

If the War Powers Act is unconstitutional, then it would almost have to follow that the Posse Comitatus Act is likewise unconstitutional, because both are acts of Congress that purport to limit the President's discretion as commander-in-chief.

[Cboldt]

If the War Powers Act is unconstitutional, then it would almost have to follow that the Posse Comitatus Act is likewise unconstitutional, because both are acts of Congress that purport to limit the President's discretion as commander-in-chief.

The War Powers act is aimed at presidential discretion in use of military force outside the territory of the United States, while Posse Commitatus is aimed at regulating the use of military power for civilian law enforcement within the territory of the United States.

IOW, the calculus is more complex than considering whether or not discretion as CinC is limited - the question involves at least "where," "under what circumstances" and "by what mechanisms" are the discretions to use military force limited.