If you want to solve a problem, it helps to be able to define it, but when it comes to a problem like China, western leaders have been struggling to find the right words. Liz Truss sought to designate China as a “threat” to Britain, but did not stay prime minister long enough for that to become established policy. Her successor, Rishi Sunak, has opted for the less combative “systemic challenge” but he is under pressure from backbench MPs to follow Truss’s path and call Beijing a “strategic threat”. Sunak has made clear he does not want the UK to...