Looking forward, Ukraine’s economy cannot support an indefinite conventional war on its own. Insurgency is an option, but sustained regular warfare probably hinges on the West’s willingness to help cover the bill. If so, NATO’s resolve (and money) will help shape the length and brutality of this war.

As long as Putin believes Russia’s military and treasury can outlast Ukraine’s, he has an incentive to wage a war of attrition. NATO could counter this incentive. A firm commitment now to pay and keep paying for the war could undermine Russia’s plan to wear down Ukraine, hastening the end of fighting.

The flip side, however, is that Western hesitancy or ambiguity about its support could coax Russia back toward that war of attrition. The U.S. just committed $40 billion to Ukraine. Britain added a further £1.3 billion ($1.6 billion). By Gorodnichenko’s numbers, that’s equal to about six or seven months of Ukraine’s war bill. Will that ratchet up the costs enough on Putin? Or will the West need to go further?