A chill is blowing through Chinese civil society as activists, journalists and academics report receiving police warnings and censorship of their social media platforms in the past few weeks as Beijing prepares to host the Winter Olympics from today through Feb. 20. In mid-January, the Beijing-based human rights activist Hu Jia (胡佳) wrote on Twitter that China’s state security apparatus was summoning activists around the country to question them and warn them to stay silent. The author Zhang Yihe (章詒和) and prominent journalist Gao Yu (高瑜) said they had lost some or all of their...