1. Congress has clearly NOT declared war.
2. Congress, through the joint resolution authorized the President to put the military into harms way, by clearly invoking the War Powers Act.
3. The Joint Resolution DOES NOT confer all the powers to the president that a Declaration of War would have, such as the authority to round up enemy non-citizens and detain them or ship them home.
4. Congress having taken up the issue, and acting with a limited authority joint resolution, the President cannot assume the state of war and assume all authority a declaration of war would confer on him. After all the Congress intentionally *did not* declare war.
JMNSHO
1) Issuing a "joint resolution" would make it appear that they are taking decisive action without having to deal with the extra political baggage that might go along with actually voting to declare war.- or -
2) Declaring war would require some effort on the government's part to determine who was actually responsible for the 9/11 attacks. In other words, a declaration of war on specific parties would put too many constraints on the actions of the federal government. By passing a "joint resolution," Congress essentially left everything open-ended. The president--and any future president, for that matter--is free to bomb anyone he pleases as long as it falls under the loosely defined "war on terror."
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3) There is a general consensus in Washington that following the Constitution is old-fashioned and too restrictive.