In a string of tweets sent from his prison cell, [Alexei Navalny,] the Russian opposition leader, called Putin “our obviously insane czar” and sent out a call to action. “We cannot wait any longer,” Navalny wrote. “Wherever you are, in Russia, Belarus or on the other side of the planet, go to the main square of your city every weekday and at 2 pm on weekends and holidays. If you are abroad, come to the Russian embassy. If you can organise a demonstration, do so on the weekend.”