There has been much excited talk of a “turning point” following Ukraine’s rapid military advances in north-eastern Kharkiv region and what Kyiv cheerily calls its “de-occupation” by fleeing Russians. Less comforting for the western democracies is an alternative theory: that the war is approaching “a moment of maximum danger”. Worries that a cornered, desperate Vladimir Putin may resort to nuclear, chemical or biological weapons have resurfaced in the US and Europe, along with the argument, articulated by France’s Emmanuel Macron, that Russia’s president, despite his terrible crimes, should not be…