The Chinese stock market has lost about $2.7 trillion in value since its peak on June 12. Government measures to bolster share prices have faltered, threatening the air of invincibility surrounding the administration of China’s president, Xi Jinping. Credit European Pressphoto Agency HONG KONG — For nearly three years, President Xi Jinping of China has crushed opposition by silencing and often locking up anyone who dares defy the government. But that aura of invincibility has been shaken by stock market speculators who have made a mockery of efforts to halt a steep slide in share prices. The losses — Chinese shares have shed more than a quarter of their value in three weeks — pose an added risk, and possibly greater danger, to a global economy grappling with Greece’s difficulties in repaying foreign loans and its possible exit from […]