I don’t really have any objection to Bush announcing that his lawyers believe he has the authority to attack Iraq without a Congressional vote. I don’t know about the de jure, but I’d bet he has authority de facto.
The legal argument rests primarily on this Congressional resolution, passed last year, which authorizes the use of armed forces against those responsible for 9/11. They’re also citing H.J. Res. 77, a Congressional resolution passed in January 1991 which authorized the invasion of Iraq.
The argument there is that the resolution is still in force; one must admit, reading the resolution, that there was no time limit involved. I have not exhaustively determined whether or not Security Council Resolutions 660, 661, 662, 664, 665, 666, 667, 669, 670, 674, and 677 have been implemented — said implementation being the specific end for which the use of armed forces was authorized. The Security Council Resolutions are available in PDF, if you want to do your own research. Most of them appear on a quick read to be quite specific to the Iraqi invasion of Kuwait, which had ended the last time I looked. However, there’re also a couple of explicit injunctions requiring Iraq to fulfil its obligations under the Vienna Convention on Diplomatic Relations and the Vienna Convention on Consular Relations and while a first glance at those shows no obvious current transgressions, this is about where I remember I don’t get paid for researching these things.
One counterargument may be found in the form of H.J Res. 109, Proposed House Resolution on Use of Force Against Iraq. Amusingly, it also cites the 1991 resolution. Unsurprisingly, since it predates today’s announcement from Bush, it doesn’t specifically address Bush’s claims.
Anyhow, as I said, I don’t object to Bush issuing press releases about what is in the end just the opinion of one set of lawyers. We’ll see what the judges say, I imagine. I just think if he’s going to make an announcement every time his lawyers back him up on a proposed plan of action, he ought to make an announcement every time his lawyers say “That’s not legal, George.”