Actually, NATO membership wouldn't mean that all NATO member states would be automatically at war with Russia on the side of Ukraine. They can just give assistance as is happening already (A5 of the North Atlantic Treaty says: "will assist the Party or Parties ... attacked by... such action as it deems necessary").

    

With NATO membership, a more stable commitment to continuing to provide assistance to Ukraine would be there.

    

Of course, there would also be a significant escalation risk. Russia, possibly, would come out making a big show of declaring war on all of NATO and, probably, issuing casual nuclear threats in response (likely not without an effect in terms of producing some knee-jerk reactions in the West) and they would probably also engage in brinksmanship to signal (bluffing) that they are truly ready to go to war with NATO.

    

In a good scenario, that would happen while no western government falls due to knee-jerk opposition and the war doesn't expand due to an implicit understanding of the parties (especially Russia) that they don't have to expand the war "just because."

    

In a worst-case scenario, Russia might actually do something crazy, either in Ukraine or, for example, in the Baltic area (or getting some other, even crazier idea). I think that not considering membership for Ukraine was partly connected to this contingency of Putin acting as a madman (genuine or role-enacted), and it is risk minimisation as such.

    

In a way, President Zelensky got the wording right when he said that uncertainty is weakness. The uncertainty created (or rather maintained, only somewhat decreased after Bucharest 2008) is due to a sense of vulnerability here, which may be warranted (we have seen highly risky moves from Russia in recent years, including covert attacks on NATO territory, e.g., in the UK, Czechia and Bulgaria, after all), but it may be seen as weakness by some in the Kremlin, no doubt.

    

And that is why my suggestion to anyone listening would have been to put a NATO mission on the ground in Ukraine (not sent into direct combat but involved in training, advising, mostly for the symbolic importance of this) to offer more than a "repeated promise". This could have sent a calibrated signal to Russia that it is getting farther from its goals, rather than closer to them, by continuing the war in Ukraine.