The purpose of sanctions is not to punish, but to apply pressure aimed at obtaining compliance, or at least compromise. The US doesn’t depend all that much on other countries for trade, and no other countries can orchestrate big international collective actions the way the US can. Imposing ineffective sanctions is, at best, a demonstration of impotence.

So there are two questions: who could have imposed meaningful sanctions on the US? The answer is probably nothing short of a concerted international effort amongst many nations. And then, the more important question, who would have imposed sanctions? Nobody, because the Iraq war had a substantial amount of international support, at least within Europe.