But I keep coming back to Chekhov. Every day that the weapons are in existence, there is a chance, however small, that they might be used. The use might be accidental. In 1995, for example, Boris Yeltsin came close to ordering retaliatory strikes over what was presumed to be an incoming American missile — which turned out, in fact, to be a Norwegian rocket monitoring the aurora borealis. We shall never know how many similar near misses there have been.

Say that, on any given day, there is a one-in-a-million chance of a nuclear weapon being used. That may sound encouraging, but, given enough time, those odds make a nuclear attack mathematically certain.

Which brings us, of course, to the present war. Putin must by now be desperate. The bribes that were supposed to have been paid to Ukrainian soldiers and officials in advance of an invasion seem instead to have gone on yachts in Cyprus. Likewise for the funds that were meant to modernize the army. On the Kremlin’s own numbers, some 10,000 Russian soldiers have died — this in a country with a very low birthrate, where many of those boys will have been their parents’ only children. Unable to broaden the war geographically, might he escalate it, first with chemical and then with nuclear weapons?