a. even congressional authorization was illegal (war of agression unless in response to an attack or against an imminent threat of an attack or specifically authorized by the UN)
Wrong, there is no legal requirement that any of those take place under US law, and the War Powers Resolution of 1973 has no such limitations, you are merely parroting well worn (and incorrect) talking points.
TH: wrong our treaty that has us participate in the UN IS US law, we cannot just ignore that law.
b. Even the congressional authorization did not actually authorize force because Iraq posed no threat in March 2003 (beyond any doubt)
Wrong. Public Law 107-243 found that Iraq was a "continuing threat" and authorized the President to use force "as he found necessary and appropriate" to protect against the continuing threat and enforce all relevant and existing UN Resolutions.
TH: Then what threat was posed by Iraq in March 2003? It was proven by March 2003 that Iraq posed NO threat to the US, Bush had no authorization to invade. and enforce UN resolutions? What UN resolution authorized the invasion of Iraq?
c. No UN resolution, Bush knew he needed second resolution, bush said he would ask for 2nd resolution (no matter what), bush drafted said resolution, bush did not ask for vote on 2nd resolution.
Wrong. JeffJ is correct, the supremacy clause rules out any need for a UN resolution, and the UN, after the fact, approved the Joint Force invasion and occupation of Iraq.
TH: your own arguement fails you. You say that the US has the right to attach whomever it chooses, you use the congressional authorization as proof that the US authorized the war, but the congressional authorization required enforcing UN resolutions, none of which authorized a use of force.
sorry you are wrong.
war was illegal.
the war was an illegal war of agression.
Iraq posed no threat and Bush invaded and overthrough the legitimate (albeit heinous) government of Iraq to (what he thought) was to install a government friendly to the US.