Pockets of Russian troops may remain to harass Ukrainian forces in the weeks ahead, but the nature of the frontline has irrevocably changed, as has its size. Kyiv is suddenly fighting a much smaller war now, along a greatly reduced frontline, against an enemy who also appear a lot smaller.

Indeed, Russia’s army relies now on forced mobilization and prisoners for its depleted ranks. Ukraine has been quite surgical, hitting supply routes to cut off already exhausted units, detecting which were the least prepared and manned. It’s been staggeringly effective and speedy.

Whether Ukraine’s counteroffensive becomes decisive rests on how far its forces are now able to push: Would going for even more territory risk over-stretch? Or is Ukraine facing an enemy that simply has no more fight left in it? No matter how over-hyped Russia’s forces became during the chaotic decades of America’s war on terror, a military that needs North Korean shells and St Petersburg convicts is at best down to the bare minimum strength needed to protect Russia itself.

So what next? Unless we see a remarkable reversal, Russia’s bid to take all of Donetsk and Luhansk regions is over. Kherson is still the focus of sustained Ukrainian pressure. And suddenly, a return to the borders Russia stole in 2014 does not seem far-fetched.

For months, the received wisdom was that Russia would “never let that happen.” But now Crimea looks oddly vulnerable — connected to Russia by the land corridor that runs along the Azov Sea through Mariupol’s coastline, and an exposed bridge across the Kerch Strait. What remain of Moscow’s over-extended, exhausted, poorly supplied and equipped forces deeper in Ukraine could face the same lethal encircling as did its supply chain around Kharkiv.

However far Kyiv pushes now, we’ve had a sea change in the dynamics of European security. Russia is no longer a peer to NATO.

Last week, Russia wasn’t even the peer of its NATO-armed neighbor — a power mostly in agriculture and IT as recently as December — that it has been slowly tormenting for eight years. The United Kingdom’s Ministry of Defense said on Monday that elements of Russia’s First Guards Tank Army — an elite unit intended to defend Moscow from any NATO attack — had been part of the chaotic Kharkiv withdrawal. They ran.

NATO member states’ defense budgets have been slowly edging toward the suggested 2% for years. But will those billions really be needed to face an army that needed shells from Pyongyang after just six months in Ukraine?

It would also be a mistake to misinterpret the silence inside Russia — a few critical analysts, politicians and talk shows aside — as a sign of a brooding, residual strength that’s about to be unleashed. This is not a system capable of looking at itself in the mirror. The Kremlin remains quiet on these issues because it cannot face the chasm between its ambitions and rhetoric, and the scruffy, hungry mercenaries it appears to have left stranded around Kharkiv.

The fact they do not speak of their errors amplifies them. The Ferris wheel that President Vladimir Putin opened in Moscow at the weekend does not become invisible when it breaks down and cannot turn. The same can be said of the monolithic and uncompromising strength Putin tries to project: when it breaks down, it is not in private.

The most flagrant foreign policy errors of the last centuries have been born of hubris, but Europe faces a series of stark choices now. Do they continue to push until Russia requests a peace that leaves its neighbors safe and the energy pipelines open again? Or do they retain the old flawed logic that a humiliated, wounded bear is even more dangerous? Would a possible successor to Putin — not that we know of one — seek a detente with Europe and prioritize the Russian economy, or prove their worth in another foolhardy, hardline act of brutish militarism?

This is also a key moment for non-proliferation and nuclear might in the post-Cold War era. What does a nuclear power do when it is vulnerable and lacking in convincing conventional might? Russia faces no existential threat now: Its borders are intact, and its military only hampered by a savage misadventure of choice. But it appears close to the limits of its conventional capabilities.

It would be a telling confirmation of the theory of mutually assured destruction that has always governed the nuclear-arms age, if weapons that could end the world as we know it remain off the table. It would also add to the possibility, raised again by the full-throated support of Ukraine by the West, that the horrors of Afghanistan, Iraq, Syria and Ukraine have not irreparably damaged the West’s moral and strategic compass, and it is still not naive to hope to see those values in action.