Vladimir Putin’s ongoing failure in Ukraine has put his strategic alliance with Chinese President Xi Jinping to the test. With Mr Putin growing ever more desperate, Mr Xi must finally realise the scale of the threat that his “friendship without limits” with the Russian president poses to China’s economic health, to global stability, and to his own geopolitical ambitions. While Mr Putin may or may not have been bluffing when he threatened to use tactical nuclear weapons in Ukraine last month, Mr Xi must assume the worst if he wants to be viewed as a responsible leader. After all, Russia’s milit…