WITH virtually all the Kremlin's opponents already jailed or in exile, and liberal press outlets and human rights groups forced to shut down, it might have appeared that years of repression in Russia had achieved their objective. But in the space of just three weeks, Russia's security services and courts have crossed several new thresholds in their campaign to destroy perceived enemies, spies and traitors. The March 29 arrest of Wall Street Journal reporter Evan Gershkovich sent a chilling warning to the few remaining Western journalists in Russia about the risks of travelling, talking to sources and simply doing their jobs. The…