Besides the fact that such a program of proxy-supply rarely works, and when it has, has usually come back to haunt us (see under: bin Laden, Osama), the idea that Kiev would emerge victorious if only we act as its principal arms supplier is fallacious simply because there is nothing that we could provide them with that Russia, in turn, couldn’t and more to the point, wouldn’t, supply the rebels. It would simply mean a net increase in armaments on both sides, which would almost certainly result in more and more civilian deaths. The simple fact of the matter is that Russia is so situated geographically that it has an overwhelming advantage over NATO in the region.
Further, even if the president went along with the McCain plan, and the United States did supply military aid to Kiev, are we so sure that their troops are equipped with the proper training to use these weapons? Doubtful. And if the United States then has to send in military advisers to train the Ukrainian troops, what happens if one of them gets killed by Russian forces? Is McCain willing to risk a shooting war—or possibly a nuclear war—with Russia over the fate of the Donbas? It would seem so.
Another objection to arming Kiev is the nature of the regime to which we are propping up. The government in Ukraine is still wondrously corrupt. It is led by an oligarch who many conveniently forget was closely tied to ancien regime, having served as minister of trade in 2012 and as minister of foreign affairs in 2009-2010.