When Vladimir Putin's gone, who comes next?

• We took a look at Putin's inner circle and opposition to see who Russia's next leader could be.
• Contenders include former President Dmitry Medvedev and Defense Minister Sergei Shoigu, one expert said.
• Some of Putin's prospective successors could be even more extreme than he is in opposing the West.

Vladimir Putin has ruled Russia for nearly two decades. But speculation over his health is reviving the question: Who will succeed Putin after he's gone?