Ukraine's lightning assault over the weekend means that for the foreseeable future the momentum in this war lies entirely with Kyiv.
Certainly, Vladimir Putin could seek to regain the initiative or at least stymie the Ukrainian advance by orchestrating an accident at the Zaporizhzhia nuclear power plant; perhaps even resort to tactical nuclear weapons.
Neither scenario is very likely. The latter could very easily see the end of his time in power - if indeed the order was even followed. Both would be stupidly reckless, although that is no guarantee Putin would not reach for them. He has form when it comes to being stupidly reckless. He did, after all, invade Ukraine.
In terms of battlefield movement therefore, where and when this advance halts will be decided by President Volodymyr Zelensky on advice from his military leadership.
The decision will largely come down to how much of an operational reserve Kyiv has.
Every military force should have a reserve: a grouping of uncommitted but highly trained and equipped troops, ready to address a number of offensive or defensive tasks as an emerging situation dictates.
The breakthrough east of Kharkiv seems to have been achieved with a force of around three brigades, or around 6,000 troops. Kyiv will need at least another brigade in reserve to be able to carry out a meaningful exploitation of Moscow's sudden collapse.
Let's assume Kyiv does have a brigade of troops ready to go, made up of tanks, infantry, artillery, engineers, air defenders and all the other parts of the military orchestra. How might they be employed?
Much depends on the new reality on the ground, which is still being carved out as Ukrainian troops harry the retreating Russian army.
Should they continue to push east into the Donbas?
Having been ignominiously ejected from the north of the country, Putin declared that "liberating the Donbas" had been the main aim of this stupid gamble all along.
It was a lie, of course. Like much else the increasingly strategically embarrassed head of state says, it was all he could grasp for in the face of Russia's first major defeat of the war.
However, Ukraine does not, for now, have to reclaim further territory in the Donbas to deny Putin the ability to declare the campaign a success; they have been achieving that since February 24. Further advance there risks losing men and material for limited additional gain, all while exposing their own logistic tail to attack from the flanks.
To the south then? Crimea is arguably Russia's centre of gravity in this war; the single location or entity that must be defended at all costs and without which the whole force crumbles.
Putin has also never relinquished his maximal aims. To snuff out Ukraine's existence as an independent and economically-viable state, Russia has to take the whole of the south, including the port of Odesa.
By threatening Crimea and denying Odesa, Kyiv could deliver the greatest strategic shock.
Getting there means a Ukrainian reserve will have to cover great distances, even if logistic support would be through friendly territory and never vastly strung out.
A Ukrainian strike south to the coast, perhaps, with the assistance of the ever-more boisterous partisans, liberating Mariupol first, followed by a swing to the west would deliver a hammer blow to Moscow.
It would also create for the Russian force in Kherson, with Ukrainian guns in front of and behind them, a situation akin to that of the German 6th Army trapped in Stalingrad in the Second World War.
And Putin - like all Russians - knows very well how that turned out.
Sign up to the Front Page newsletter for free: Your essential guide to the day's agenda from The Telegraph - direct to your inbox seven days a week.