There were fireworks in Moscow as the Russian military retreated hastily from the key town of Izyum in Ukraine’s Kharkiv region on Sept. 10. The Russian capital wasn’t actually celebrating the debacle: The display was part of its City Day festivities. But there could hardly be a better illustration of the Putin regime’s utter unpreparedness for defeat. Its attempt to prosecute a war of invasion while keeping up the appearance of life going on as usual was doomed from the start — and the choices it faces now are stark.

In a matter of days, Ukraine pushed the Russian troops out of the Kharkiv Region. This may not look like a major victory in terms of territory regained — some 2,500 square kilometers, or a little more by now, out of the 125,000 square kilometers Russia held in Ukraine before this week. Yet Ukrainian and Western jubilation is justified.

The Kharkiv region has historically been ruthless to hubris. As Russian forces were routed there in the last few days, many commentators recalled the disastrous 1942 push by Marshal Semyon Timoshenko against a smaller German force in the area, which deftly moved to cut off Moscow’s forces off from the north. Some 250,000 Soviet troops were taken prisoner. The fiasco opened the path for Hitler’s armies to reach Stalingrad, where they were only stopped at an enormous cost in human lives.

The current Russian setback, too, is strategically significant. The loss of the Kharkiv positions turns the goal of encircling Ukrainian forces in the Donetsk region into a pipe dream: Russian troops can no longer press on from the north. The invading army retreated to avoid being blocked from supply lines and reinforcements. However, the Russians couldn’t avoid damage to their already low morale.

Putin’s soldiers are digging in on the eastern bank of the river Oskil, but the defensive positions lack depth, just as they did around Izyum. The Russian forces — including those in areas held by Russian proxies since 2014 — will be vulnerable to further Ukrainian counterattacks, which are expected now in both the Luhansk and Donetsk regions.

These thrusts will seek to take advantage of what may prove to be Russia’s biggest mistake of the entire hubristic and fratricidal campaign. Since the retreat from Kyiv and northern Ukraine in April, the Russian command has used the fighting forces of the self-proclaimed Luhansk and Donetsk People’s Republics as cannon fodder. By doing so, they have lost thousands of the only soldiers who had skin in Putin’s game: These fighting-age men were anti-Ukrainian by definition — and committed to combat as fiercely as Ukrainians themselves. Few Russian soldiers could match their determination. When Kyiv began its counterattack, the Luhansk and Donetsk fighters had been nearly eliminated by attrition.

Indeed, the positions in the Kharkiv region were manned by Russia’s regular military, fighting for cash: They folded without putting up much of a fight when Ukrainians pushed hard enough.

Now, the Luhansk People’s Republic, “apart from frontline areas, is probably empty of manpower,” tweeted Polish military analyst Konrad Muzyka, one of the most astute observers of the campaign. Fighting-age males were drafted in large numbers in the past few months, he said, meaning “there are no men to fight in Luhansk.”

To hold on to the bulk of the conquered territory, Russia urgently needs to shrink the front and bring in reserves. It’s going to be hard to do either fast enough to counter Ukraine’s momentum. Even a general mobilization would now come too late to prevent further defeats. The Russian far right has insisted from the start it would be necessary to win the war.

Now, even those locals who otherwise would have welcomed a Russian takeover will withhold their support. They will either lay low or aid Ukrainian guerillas. The loud assurances of many a Russian functionary since February that “Russia is here for good” ring hollow as the cars of fleeing collaborators line up on the border near Belgorod.

Further supplies of sophisticated Western weapons are now assured for Ukraine. Kyiv has proved it’s able to fight back and win, so there’s no reason for NATO to doubt the efficiency of its aid.

In Russia, meanwhile, an angry and aggrieved extreme nationalist community is rapidly turning into a threat to the regime. Since the start of the invasion, it’s been the only one allowed relatively free expression because it is staunchly pro-war. The narrative dominant on the far right on Telegram channels is now full of indignation over the incompetence of the corrupt military and political leadership. They are propagating a backstabbers theory focused on leaders of the “special military operation” who aren’t ethnic Russians —like Defense Minister Sergei Shoigu, who is from Tuva near Mongolia — or Chechen leader Ramzan Kadyrov. Given the ultranationalists’ high support in Russia’s all-powerful law enforcement agencies, it’s conceivable that discontent may be brewing among the very forces on which Putin has relied to hold on to power.

It’s too early to predict a military rout for the entire Russian force in Ukraine, let alone a regime collapse. But suddenly, those are glimmers of possibility thanks to what is essentially a local Ukrainian success. This is a consequence of the most fundamental flaw in the thinking behind Putin’s Ukraine campaign — if there was any thinking done at all amid all the imperialist emotion. Russia never took its opponent seriously, never even considered Ukraine a viable entity. So it never contemplated the possibility of defeat.

No plans were made for pessimistic scenarios — and none seem to exist today. In a war, the side that isn’t prepared for setbacks can come apart at the first signs of trouble; overconfidence and panic are opposite sides of the same coin. Russians went in without the will to win, but they were also not primed for the risk of losing. Any setback then becomes a catastrophic blow to national pride. This will rankle even if Russia manages to halt Ukraine’s current momentum. These factors could be the ingredients of a historic defeat.