Former Kremlin leader Dmitry Medvedev issued threats on Sunday to former Russian political prisoners who were released into exile as part of a prisoner exchange with the West. Medvedev called the opposition figures “traitors” who “pose an existential threat to today’s Russia,” in a post on Telegram. “They should not forget the transience of their existence in this world,” he said. Medvedev, who now serves as deputy head of the Russian Security Council, advised them to always look around with caution. The Russian politicians and activists released in the deal include Vladimir Kara-Mursa, Ilya Y…