Well, what are we talking about? Are we talking about behaving as you please worldwide or are we talking about a veto about the national security of the US? If we were talking about the first, you could indeed leave NATO, the UN, the OSCE, because talking would make no sense anymore. If we were talking about the latter, your given example of Kosovo is not fitting, because the situation in Serbia never posed a threat to the alliance. I agree with you that some nations in the alliance have consistently undermined the efforts in the war and cooperated with the enemy. Though, it was not a veto.
By tinkering with the campaign plan and leaking targeting data they did, in effect, veto the plan because it was no longer an effective option.
BTW, you write well.