Ukrainian President Petro Poroshenko visits Washington on Thursday . The U.S. and Ukraine have been at odds over the crisis in eastern Ukraine, where pro-Russian separatists are fighting government forces for control of a swathe of territory. The truce is shaky , but the Ukrainian president seems intent on pursuing a peaceful settlement . Obama should agree to provide defensive arms on an expedited basis , authors say . Talbott and Pifer : Moscow has grossly violated the Budapest memorandum .
Ukrainian President Petro Poroshenko visits Washington on Thursday . The U.S. and Ukraine have been at odds over the crisis in eastern Ukraine, where pro-Russian separatists are fighting government forces for control of a swathe of territory. Obama should agree to provide defensive arms on an expedited basis , authors say . Talbott and Pifer : Moscow has grossly violated the Budapest memorandum .