There’s a diplomatic time bomb quietly ticking away on Vladimir Putin’s desk, buried under the casualty reports, gloomy economic figures and other products of his failing invasion of Ukraine. It is not yet urgent, but it can’t be ignored forever. In August, South Africa will host the BRICS Summit, an annual meeting with the leaders of Brazil, India, China and, crucially, Russia. Putin must decide whether or not to attend. It’s an impossible choice, in a sense, because both options carry risk. On one side of the scales is the Russian President’s ego and already tarnished reputation. On the other...