That's a copout answer. We shouldn't hide behind us not being contractually obligated to intervene to do the right thing. To your point, do you believe that NATO will admit Ukraine during an active war, which would be tantamount to a declaration of war on Russia?

As an aside, it seems we already screwed Ukraine over--when the USSR collapsed and Ukraine declared sovereignty, we got Ukraine to give up the nuclear arsenal it inherited by pledging, but short of a treaty, to protect them from aggression by Russia...