The USA failing to fulfil its international obligations? Perish the thought. For example it's obligations under the UN Charter.

"Serious consequences" quite intentionally left it open for those consequences to be determined at a future time. And the only body with the authority to determine what that action should be, and whether it was justified, was the Security Council, not the government of individual countries.

It was on that understanding that Resolution 1441 was approved, as a way of holding back the rush to war, and of putting additional pressure on Saddam to cooperate in demonstrating that he had in fact complied with earlier resolution to get rid of his weapons of mass destuction.