Funny, I've never heard or read anything about them doing this.
An interesting bit in http://www4.law.cornell.edu/uscode/50/1541.html is that the US president can perform an "introduction of United States Armed Forces into hostilities" without Congress declaring war, if a national emergency is in effect. So the war in Iraq would seem to be essentially legal from a POV of US law. I previously thought that only Congress could do this. National emergency is a very interesting bit of the code to have if you have either a friendly majority in both houses, or if opposing you would be seen as political suicide, as was the case in late 2001... I wonder if the powers conferred include anything like law enacting with Congress bypass (for speed, you know, we don't want Congress delaying this very important new bit of anti terrorist press quashing law...) -- Vincent Penquerc'h