2. Limited lethal military assistance, whether offensive or defensive, won’t impose sufficient costs on Russia to deter its support for separatists. Providing weapons to the Ukrainian military may indeed impose greater costs on Russian forces. However, because Washington has limited its own options, Moscow could escalate its support for rebel forces and counter whatever the United States might provide without great fear of the consequences. Worse, providing lethal military assistance to Ukrainian forces or—in other words—helping Kiev to kill more Russian soldiers, could actually change the way many Russians see the conflict. We should certainly expect Russia’s state-controlled media to exploit such an opportunity to the greatest possible extent. Anti-Americanism is already at new highs in the country, with over 80 percent of Russians expressing negative views toward the United States and 42 percent seeing it as “hostile” in a recent poll by the respected Levada Center.

Imposing sufficient costs to deter further Russian support for the separatists and their offensive operations requires making the political cost of that support higher than the political cost of stalemate or a separatist defeat. Yet an American decision to impose costs that high in Ukraine would allow the Kremlin to frame the war as an existential U.S.-Russian conflict, rather than as a symbolically important but otherwise optional struggle to help Ukraine’s separatists. Turning the conflict in Ukraine into an anti-American war might dramatically increase the price that Russians are willing to pay—and thus make it easier for Russian president Vladimir Putin to send more troops and weapons into Ukraine, to marginalize the limited opposition that now exists and to persuade Russia’s citizens to endure greater hardship from Western sanctions. It would also give Putin an incentive to acknowledge Russia’s role openly, something that could make negotiations to end the fighting even harder.