"When the President takes measures incompatible with the expressed or implied will of Congress, his power is at its lowest ebb." —Justice Kennedy, citing Justice Jackson
Justice Kennedy on this own:
This is not a case where the Executive can assert some unilateral authority to fill a void left by congressional inaction. It is a case where Congress, in the proper exercise of its powers as an independent branch of government, and as part of along tradition of legislative involvement in matters of military justice, has considered the subject of military tribunals and set limits on the President's authority.