Um, the Congress has the unambiguous power to declare war. Full stop. It gave this power up after 1941. The 1973 rule didn't go nearly far enough in reining in the bipartisan imperial project. That's the main problem. The solution is not to assume that the President controls war power. He doesn't. He's commander in chief once a war starts. That's it. Defense of the country from attack or imminent (i.e., really imminent, not propaganda-based) attack is not at issue. Go and defend and send a message to Congress to declare war. Non-state actors? Not a fatal problem. Any and all parsing should start from the obvious and utterly crystal clear delegation of war-making powers to the Congress. Read the debates, the Federalist. Clear as day.
Update: Here's another take on the War Powers Act, from the Constitution Project.
Update: Here's another take on the War Powers Act, from the Constitution Project.