Arming the Ukrainian government would be a mistake

To be succinct on this point, the principal reason why Ukrainian governmental figures like Prime Minister Yatsenyuk are presently beating the drum to Washington that the Russian military is directly intervening in Ukraine is because the Ukrainian military has suffered a number of setbacks in its efforts to repel an offensive of rebel pro-Russian forces in Donetsk and Lugansk over the closing weeks of January.  It would appear that they are currently losing control of a key crossroads and line of communication between rebel strongholds in Donetsk and Lugansk in the Debaltseve salient.  They have fallen back from Donetsk's airport, and Mariupol has come under attack.  Pro-Russian militias, armed with substantial quantities of Russian equipment, are making significant offensive gains, and the government of Kiev wants to counter these gains with more advanced tactical weapons systems from the U.S. 
             On this point, it is one thing for NATO to beef up rapid reaction forces in Eastern Europe and the Baltic States, and such a move might be a necessity in the near term, in view of North Atlantic Treaty obligations to protect Poland and the Baltic States from Russian aggression.  Ukraine, at the present moment, is not a NATO member state and it would be a provocation against Russia to treat it like one.  Under the present government of the Russian Federation, any move to incorporate Ukraine into NATO or to provide lethal military assistance or advisers to Ukraine would necessarily be viewed as a hostile act against Russian security interests, inviting direct and unvarnished Russian military intervention into eastern Ukraine and forcing the hand of the Obama administration - act to vigorously defend a country in Russia's traditional sphere of influence or risk a perception of American military weakness and a political victory for Putin, snatched from the jaws of defeat through sanctions and cheap oil.  In other words, if American weapons find their way to Ukraine, it will certainly lead to a situation in which the U.S. will, invariably, lose!
               Moreover, as I have heretofore stressed in regard to this conflict, it would seem that the Ukrainian government has persisted in its hard line stance toward countervailing perspectives on economic and cultural development in the Don basin since the Euromaidan revolution.  Emphatically, Kiev needs to pursue new strategies seeking to placate local demands in the eastern oblasts for greater autonomy relative to Kiev on economic and cultural/linguistic matters.  To be clear, I do not know exactly how such a strategy might be prosecuted or, in fact, who the Poroshenko government should negotiate with in order to undertake a shift in emphasis from militarily holding and retaking ground to negotiating the terms of a constitutional devolution of authority onto local actors, otherwise committed to the notion of remaining within Ukraine.
              The pro-Russian rebel leadership in the Donetsk and Lugansk People's Republics have made it clear that their intention is not to remain within Ukraine.  On the other hand, it is not clear what relationship these individuals have to local populations in the eastern oblasts or whether they actually enjoy anything close to resembling a democratic manadate to speak for the Ukrainian citizens in these oblasts.  As such, the very individuals with whom Kiev might need to negotiate a new cease fire are the last people with whom it should be discussing the long term future of Donetsk and Lugansk.  On the contrary, if Kiev is to be serious in engaging the eastern oblasts with a more open mind toward limited autonomy, it might be more successful in doing so in areas of the Don basin and in other eastern oblasts (e.g. Kharkiiv) in which the central government is already safely in control.  And if the central government makes a tangible effort to meet pro-Russian populations in areas under its control half-way, then it might make some in roads in convincing populations in areas currently under rebel control that the latter do not bear their best interests at heart! 
               Respecting the need for the Poroshenko government and other key actors in Kiev to find new ways of engaging with local populations in the eastern oblasts that will respect the rights of these populations to democratic self-government, I cannot see how American efforts to provide lethal military hardware to Kiev will achieve a viable political solution to the war in Donetsk and Lugansk.  Acknowledging, moreover, that the bulk of rebel forces in these oblasts are likely composed of citizens of the Russian Federation and that these entities have likely been armed by the Putin government with a variety of both antiquated surplus arms and newer materiale, I feel less certain that substantial quantities of Russian professional military forces are engaged in the fight for Donetsk and Lugansk.  The key point is that rebel forces, whatever their composition, are on the ground, engaged in offensive operations, and currently making substantial gains.  To the best of its ability, Ukrainian military forces need to stabilize the situation, without any substantial assistance from the West, and engage in new, constitutionally innovative strategies with viable local partners intended to politically marginalize Russian nationalists on Ukrainian soil.  In the meantime, the U.S. and EU need to continue to contemplate their options to economically punish the Russian Federation for its behavior in regard to Ukraine and seek to open the possibility for a peaceful resolution, through negotiation with the Russian Federation and the Ukrainian central government.