Russian opposition leader Alexei Navalny is the most resilient opponent Vladimir Putin has ever faced. Navalny survived assassination by Novichok, returned to Russia and is now in a prison cell. Stephen Sackur speaks to Navalny's chief of staff Leonid Volkov. The opposition movement has supporters willing to take to the streets in anti-Putin protests in Russian towns and cities; but do they have a strategy capable of forcing Putin out of power?
