I was under the impression that when Iraq surrendered it had agreed to conditions regarding weapons of mass destruction and allowing of inspectors ensure this Iraq continued to not make or store them.
If this is true, wouldn't not complying with the terms of surrender allow us to use miltary means to bring about this compliance?

Also would not a state that had engaged in an assassination attempt be regarded as having engaged in an aggressive act. What recourse is allow if a state plots and attempts to carry out assassination against heads of state (or former heads of state) of another country?

Another aspect is that we are already engaged in warfare with Iraq- we have fighter planes attacking targets and being shot at in the No Fly Zones- established by Iraq's surrender. Plus we have an embargo, which is also an act of war.
So what is the problem with "starting a war" when we are actually already in the middle of one?
The only real question is are other countries willing to support our effort to either make Iraq comply with existing agreements, or if this isn't going happen, make Iraq follow these agreements by using warfare to bring about compliance to these conditions.