There are plenty of differences between Gorbachev’s Soviet Union and Xi’s China. But there are enough similarities that Xi should be worried.“The nuclear meltdown at Chernobyl” – wrote former Soviet leader Mikhail Gorbachev, on the eve of the 20th anniversary of the nuclear disaster – “even more than my launch of perestroika, was perhaps the main cause of the Soviet Union’s collapse five years later.” He went on to write that “the Chernobyl catastrophe was a historic turning point: there was the era before the disaster, and there is the very different era that has followed.” While the outcome from...