Spare a moment, please, for the lame-duck superpower. It calls itself the leader of the free world, but the free world no longer believes it. When it extends its hand, nobody rushes to accept. When it threatens, nobody trembles. After President Trump arrived in Beijing this week, Xi Jinping showered him with pomp befitting a summit of great powers. Yet the Chinese leader permitted potshots at his guest to go viral on his country’s internet rather than suppressing them, as some observers