It's been an action-packed week for negotiations over the conflict in Ukraine. On Monday, Kurt Volker, the U.S. special envoy to Ukraine, met with Russian presidential aide Vladislav Surkov in Belgrade, Serbia, to discuss Moscow's proposal for a U.N. peacekeeping force in eastern Ukraine. Two days later, Russian President Vladimir Putin called the leaders of the self-proclaimed Donetsk and Luhansk people's republics to discuss a prisoner swap between the separatist territories and Ukraine. Then on Thursday, a spokeswoman for the Ukrainian security services confirmed that Kiev was ready to engage in such an exchange. In and of themselves, these developments don't portend a major breakthrough in the nearly four-year-old conflict in eastern Ukraine. Prisoner swaps with separatist forces have occurred several times before, and meetings between U.S. and Russian officials over the struggle are hardly uncommon. Nevertheless, the context and timing of these events suggest that they may be more than...