The basic form of that off-ramp is clear, but getting it in place won’t be easy. A plausible settlement might look like this: a withdrawal of Russian forces, a commitment by Ukraine to stay out of NATO and remain non-aligned, the ceding of the Eastern separatist statelets to Russia, and security guarantees to assure Ukraine of its independence from Russia.

Supposing for the moment that Putin would go along, the big political objection is obvious: He could present this as victory. It’s what he wanted from the outset, he could say. It’s what the allies refused to discuss — and it took Russian arms to bring Ukraine and its friends to their senses. For Ukraine, it would feel like defeat: Our sacrifice was for this? And for Western politicians, it would be a hard thing to explain.

But they and Ukraine’s government need to weigh the alternatives. Are they sufficiently confident that Putin can be overthrown, or made to yield unconditionally, without a wider war, perhaps involving nuclear weapons? Is drawn-out low-level warfare confined to Ukraine really in Ukrainians’ best interests? Is the outright subjection of Ukraine, if Putin prevails despite everything, better than Finlandization? And how long can the allies maintain their sanctions once the toll on their own economies and financial systems becomes more apparent?