If the UN was some sort of real power in the world, it might be. However, it is really only as powerful as the US military makes it, and the current administration has a very dim opinion of the importance, the usefulness, and even the necessity of the UN.
US foreign policy since WWII has been to maintain hegemony by (successfully) gently discouraging European military strength. The power of the rest of the membership is limited by design and has led to quite a lot of world peace. If you want evidence look at the long list of treaties the US has not signed [1] in order to not lose sovereignty to the international community.
There are some real limitations in matters of range and equipment. They are not allowed to have aircraft carriers or cruise missles. IIRC, they are not allowed bomber planes as well. Tools of projections are forbidden.
Off topic, but let me throw a few bits here. It's certainly not a US tool, not like NATO is: when UN security council vetoed (Russia, China) bombing of Serbia and Montenegro in 1999, US/NATO went ahead anyway.
But when appropriate, US govt will pull out a UN card. When not, it will be simply disregarded.
So UN doesn't have any power in the real sense: Serbia has been relying on that power yet there's this now practically independent state of Kosovo created against UN rules. Not that I agree with the rules (hopefully we can amend them so there is a viable way for regions to split out of their parent countries, thus avoiding wars).
I'm not sure why this comment is being down voted. I think it's a significant aspect of today's geopolitics that US, arguably after having become an exporter of oil, is becoming protectionist and is actively showing disinterest in foreign cooperation. Given that some of these world-police organizations (forgive the lay-man expression) heavily rely on US, this is pertinent.
