Really: Could Specter please show us where in our Constitution it says that the Senate shall share responsibility with the President as Commander in Chief of our armed forces?
The decision of whether or not to go to war in Iraq was already decided as a shared and joint responsibility, Senator Specter. Perhaps you don't remember when the United States Senate voted to give President Bush the authority to invade Iraq. Small detail most in Congress now want swept under the rug. As to whether or not the president is the sole decider....well, it's always been that way. The president is the commander-in-chief. That's what the Constitution says, as much as Democrats hate the whole idea.
So what can the Congress do? The Congress does have the power of the purse. To that end, that makes them somewhat of a decider in the whole matter. But they know they don't have the votes to pull the funding for the war, nor would that sit well with the American people. There's not much they can do.
All they can do is sit around and pass non-binding resolutions against the war. That's not much of a decider, now is it?