At the recent Valdai Discussion Club, I asked Russian President Vladimir Putin if he would be open to meeting Chinese President Xi Jinping and US President Donald Trump at the Asia-Pacific Economic Cooperation (Apec) forum in Shenzhen. I also asked, more broadly, what role China could play in promoting peace in Ukraine, mediating and contributing to peacekeeping. Putin was receptive, warmly welcoming the idea of a China-hosted meeting. Trump, too, has expressed a willingness to meet Xi and...