LONDON, July 3 (Reuters Breakingviews) - The failed mutiny against Vladimir Putin hasn’t just weakened the Russian president. It is also a setback for his most important ally, Chinese President Xi Jinping. At the same time, China is grappling with a weaker economy and confronted by a stronger American-led alliance. It no longer seems certain to become the world’s top power. China remains a threat, notably to Taiwan. So the United States and its allies can’t let their guard down. But the new situation may open up chances to work with China on peace and climate change. The mood has...