How to deter Vladimir Putin from invading Ukraine

IN CHRISTMASUSSR 1991 the Soviet Union ceased to exist. Mikhail Gorbachev, its last leader, said that, even if the future was uncertain, at least “we have…abandoned the practice of interfering in others’ internal affairs and using troops outside the country.”Thirty years later Russia, the heir to the old Soviet Union, is once again in the business of interfering abroad. In Vladimir Putin, it is run by a man who splenetically regrets the dissolution of the . Mr Putin particularly resents the way two Slavic states, Ukraine and Belarus, . He has recently reasserted a large degree of influence over Belarus, after its election-rigging despot turned to him for help. And he is massing troops on Ukraine’s border—over 70,000 of them, complete with supply lines, field hospitals and the prospect of reinforcements. American intelligence fears that he could invade Ukraine soon. What can be done to deter him?