Possibility... the reality is a resolution made by the un security council can get us into a war/conflict without any vote by congress. Congress in 1945 delegated its war powers.
Quote from AAAintheBeltway:
I think the argument would be that if the US started a war that had not been approved by the UN or if had been specifically disapproved by the UN, then the US would be acting in violation of international law.
While we could thumb our noses at that, violation of international law could have cosnequences, eg officials could be subject to arrest outside the US and prosecution.