--constitutional scholars. The framers of the constitution did not envision a standing military like that of the modern U.S., nor did they imagine that the U.S. military would one day be used by the executive branch as an instrument of foreign policy rather than in defense of the Constitution.
http://en.wikipedia.org/wiki/War_Powers_ResolutionThe War Powers Resolution has been controversial since it became law, because it did not settle the question of the Constitutional division of powers between branches of U.S. government with regard to the declaration and the conduct of war. See Separation of powers under the United States Constitution for more on this topic.
Though not a formal declaration of war, there remain underlying questions that its constitutionality is consistent with the provisions of the resolution. The reports to Congress required of the President have been drafted to state that they are "consistent with" the War Powers Resolution rather than "pursuant to" so as to take into account the Presidential position that the Resolution is unconstitutional.
One argument for the unconstitutionality of the War Powers Resolution — Philip Bobbitt's in "War Powers: An Essay on John Hart Ely's War and Responsibility: Constitutional Lessons of Vietnam and Its Aftermath," Michigan Law Quarterly 92, no. 6 (May 1994): 1364–1400 — runs as follows: "The power to make war is not an enumerated power" and the notion that to "declare" war is to "commence" war is a "contemporary textual preconception"; the Framers of the Constitution believed that statutory authorization was the route by which the United States would be committed to war, and that 'declaration' was meant for only total wars, as shown by the history of the Quasi-War with France (1798–1800); in general, constitutional powers are not so much separated as "linked and sequenced"; Congress's control over the armed forces is "structured" by appropriation, while the president commands; thus the act of declaring war should not be fetishized. (Bobbitt, the nephew of Lyndon Johnson, also argues that "A democracy cannot… tolerate secret policies" because they undermine the legitimacy of governmental action.)
A second constitutionality argument concerns a possible breach of the 'separation of powers' doctrine, and whether this Act changes the balance between the Legislative and Executive functions. The President is bound by an Oath of Office: "I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability; preserve, protect, and defend the Constitution of the United States." (US Constitution, Article 2, Section 1, Clause 8). This type of constitutional controversy is similar to one that occurred under President Andrew Johnson with the Tenure of Office Act (1867). In that prior instance, the Legislative branch attempted to control the removal of Executive branch officers. Here, the separation of powers issue is whether the War Powers Resolution requirements for Congressional approval and Executive reporting to Congress change the constitutional balance established in Articles I and II, namely that Congress is explicitly granted the sole authority to declare war while the Executive has inherent authority as Commander in Chief. This argument does not address the other reporting requirements imposed in executive officials and agencies by other statutes, nor does it address the provisions of Article I Section 8 that give Congress the authority to "make Rules for the Government and Regulation of the land and naval Forces". The argument raises the issue of the executive's inherent authority as Commander in Chief, without addressing whether (or when) any other military commanders may ignore such rules, or whether (and when) only the Commander in Chief would not be bound by such rules. The US Supreme Court has not ruled on these issues.
There is also an unresolved legal question, discussed by Justice White in INS v. Chadha of whether a "key provision of the War Powers Resolution", namely 50 U.S.C. 1544(c), constitute an improper legislative veto. (See Chahda, 462 U.S. 919, 971). The provisions in that section 5(c) state "such forces shall be removed by the President if the Congress so directs by concurrent resolution". Justice White argues in his dissent in Chadha that this is a violation of the Presentment clause. The majority in Chadha does not resolve the issue. Justice White does not address or evaluate in his dissent whether that section would fall within the inherent Congressional authority under Article I Section 8 to "make Rules for the Government and Regulation of the land and naval Forces."