Congressional approval wasn't needed. New was wrong, and by refusing to hear his case the Courts agreed that he was wrong.
Yeah, ok. I just showed you written law that specifically says that Congressional approval is necessary and your response is 'no it isn't' and 'New was wrong'. Great argument there.
It cannot get any clearer than the law I just showed you. I don't know if you're choosing not to see it, or if you really can't make the distinction between serving under US law and serving under UN law. Regardless of how you think US soldiers should be allowed to be dispatched, the law says what it says. New was absolutely right.