Navalny is the only figure with any chance of unseating President Vladimir Putin in the 2018 elections

It was an overcast afternoon in northern Moscow on April 10, and a crowd was gathering outside the jail where Alexei Navalny, the Russian opposition leader, was finishing yet another stint behind bars. The crowd, mostly opposition activists and journalists, was expecting to hear a fiery speech from Navalny, a 40-year-old anti-corruption activist. But there would…