Hundreds of teenagers waited hours outside Russia’s Supreme Court to witness the only antiwar party lose its place on the ballot. Then a police officer raised a megaphone to talk about draft offices.

All day on August 10, Russia’s Supreme Court heard a lawsuit seeking to revoke the Yabloko (“Apple”) party’s registration for the State Duma elections. Hundreds of people stood outside the courthouse on Povarskaya Street the entire time, supporters of the only antiwar party that could theoretically participate in the vote. Most were Muscovites under 30, many of them teenagers. For many of them, it was their first street protest; some were not even old enough to vote in September. They passed ...