Senate candidate Rand Paul (Republican - Kentucky) has stated on his campaign site possibly the best summary of war powers I have seen:
The Constitution explicitly grants Congress the power to declare war. As James Madison wrote, “The Constitution supposes, what history demonstrates, that the executive is the power most prone to war. The Constitution has, therefore, with studied care vested that power in the legislature."
However, in the face of an imminent nuclear attack or in response to an assault, the executive [Presidential] branch can and should make military responses without Congressional authority. After 911, an immediate raid by 10,000 Special Forces on camps in Afghanistan would have been justified by the executive, even if the decision was made in secrecy.
But, any military action that takes more than a few days or weeks to organize and is directed against a country's government should require a declaration of war. When Japan attacked Pearl Harbor, Congress met and declared war within 24hrs.
Congress has had plenty of time to declare war on Afghanistan and Iraq. As a member of Congress, Dr. Rand Paul would have demanded and voted in the affirmative for a declaration of war with Afghanistan. He would demand and voted against a declaration of war with Iraq.
To the average individual, this may seem like a minor issue, if not irrelevent to their lives. But one must realize the extreme costs, both in human lives and cold hard cash, as well as possibilities of future repercussions due to our actions (see blowback). I urge you to at least keep this in mind and question the actions of both our Presidents and Congress when you get in a debate about whether or not war is just. The question should be: did we even follow the Constitution when we got involved in the war in the first place?