Once we have eliminated all the impossible scenarios, the least improbable outcome of the war in Ukraine is a Russian victory. Any conceivable Russian victory now will entail such a loss of blood and treasure that it will have to be judged Pyrrhic at best. But it will be a victory nonetheless — and we in the West had better come to grips with that hard truth. Let’s begin by eliminating the impossible. The first unrealistic endgame is the reduction of Ukraine to a vassal state of the Russian empire. The second impossible scenario is the total defeat of the...