If crises should not be wasted, then the war in Ukraine might already have offered an opportunity — to remake the United Nations whose charter today lies in tatters. That is what we take from the astonishing demarche Thursday by Ukraine’s ambassador, Sergiy Kyslytsya, in a meeting of the Security Council, presided over by Ukraine’s enemy, the envoy of Russia. It was first reported by our Benny Avni in Thursday’s Sun.

The gist of the report is that Ukraine is challenging the right of Russia to preside over the Security Council while it’s discussing an attack on Ukraine that Russia is pressing in violation of the United Nations Charter. It’s more than that, though. Ukraine is questioning the very right of Russia itself to be a member of the Security Council and even of the General Assembly. It might be one of the great diplomatic moves of our time.

That Russia has no business presiding over the Security Council while it’s hearing complaints about Russia’s own actions strikes us as an easy call. Russia ought — or be forced — to recuse itself and let another country do the presiding, a task that rotates among the members anyhow. The question of whether Russia was ever properly admitted to the world body, though, is another matter altogether — and could be a hard hill to climb.

Then again, so is K2, and it’s been hiked. What the Ukrainians are arguing now is that Russia was never properly admitted to the United Nations in the first place. The seat at issue was originally given to the Union of Soviet Socialist Republics. Russia was one of the socialist republics, but so were, say, the Byelorussian Soviet Socialist Republic or the Armenian SSR or even the Ukrainian SSR.

So where did Russia come off claiming in the UN the seat of the USSR? Ukraine points out that there was, in fact, no vote in either the Security Council or the General Assembly in respect of handing the USSR’s membership in the United Nations to Russia. The issue simmered for years. One ex-envoy to the world body from Israel, Yehuda Blum, wrote a note on the matter in the European Journal of International Law.

It centers on the days leading up to Christmas 1991, when the transitional Soviet leadership suddenly realized the implications of the USSR’s collapse. So the President of the Russian Federation, Boris Yeltsin, wrote to the UN secretary general, asserting that the USSR’s membership in the UN would be “continued by the Russian Federation with the support of the countries of the Commonwealth of Independent States.”

Yet, demurred Ambassador Blum, a particularly scholarly diplomat, the “correct legal path to this end would have been for all the republics of the Soviet Union except Russia to secede from the union, thus preserving the continuity between the Soviet Union and Russia for UN membership purposes. For reasons of Soviet domestic politics such a solution was apparently not feasible.”

The result, Mr. Blum concluded, was a “practical solution, which, while politically the only realistic one, remains legally suspect.” Or in other words, a dead letter. And it’s a diplomatic, legal, and even constitutional vulnerability that France, Britain, and America would, in our view, be wise to exploit at every turn. Russia might try to veto them in the Security Council, but we could reply that it lacks the standing to do so.

That leaves the question of China. It turns out, of course, that China’s own standing within the United Nations is open to question. That’s because the People’s Republic of China was also never properly admitted to the United Nations. This is why Article 23 of the UN Charter still lists the Republic of China, meaning Free China, as a permanent member of the Security Council.

Pressing the case against Russia and China at the UN, we fully comprehend, will be met with resistance. All the more reason to start it now. It’s a campaign that would logically be supported by admirers of the idea of the UN, in that one, if only one, of the reasons the UN is so despised is the Russian and Communist Chinese vetoes. In the long run, we favor ending the UN. Meantime, let the crisis in Ukraine not be wasted.