Just about everyone reckons Vladimir Putin is in deep trouble in Ukraine. Everyone – meaning Volodymyr Zelenskyy, his European backers and western military analysts and commentators – seems to believe Russia’s dictator is heading for humiliation. They could all be wrong, of course. But what if they’re right? How might a desperate, cornered Putin, fearful for his policy and person, react to the prospect of defeat? On past form, he will escalate, not capitulate. His options range from trolling YouTube to waging nuclear war.

For Ukraine, the latest news is mostly good. Using sophisticated Ukrainian-made drones and missiles, it has forced the invaders on to the back foot. Russia’s tally of dead and wounded is said to be running to 30,000 each month. Its advance has stalled – and in some places has been reversed. Ukrainian airstrikes deep into Russian territory are bringing the war home to a misled, disillusioned public. St Petersburg burns. Fuel shortages cause panic buying. Prices and taxes are rising. Putin’s 2022 “special military operation”, which was supposed to bring swift victory, has now lasted longer than the first world war.

Ukrainians still suffer daily, ever more indiscriminate air attacks. But speaking to the Guardian last week, Zelenskyy sounded optimistic that the nightmare may be near an end. His view is backed, up to a point, by western experts. Jack Watling, a land warfare specialist at the Royal United Services Institute, wrote this month that Russia’s battlefield combat power is faltering and a ceasefire may be within reach. “Putin’s savagery is exceeded only by its futility. Slowly but surely, he is losing his war,” wrote the US commentator Seth Stodder.

All well and good. But three awkward questions arise. First, does Putin actually realise he’s losing? Russia’s leader is a conservative, old-school thug. He thinks Russia is still a superpower, not what he’s made it: a despised rogue state and Chinese client. Out-of-touch Putin doesn’t use a smartphone or the internet. He’s said to rely on inner circle apparatchiks, loyalist generals, spies and state media, who tell him what he wants to hear. If so, he’ll just keep going regardless.

Yet this assessment raises a second, alarming question: what will Putin do if and when his Kremlin bubble bursts and it suddenly dawns on him that a devastating strategic and personal defeat looms? Don’t expect him to sue for peace. Only last week he contemptuously dismissed Zelenskyy’s offer of ceasefire talks, stubbornly reiterating his war aims wishlist.

Putin’s more probable reaction would be to double down by expanding the active war zone beyond Ukraine, potentially drawing European Nato member states into the open-ended, direct confrontation they have avoided until now. In many respects, this is already happening. Hence a chorus of urgent warnings from European security, intelligence and military chiefs about how Russian sabotage, subversion and coercion are accelerating, the more it struggles in Ukraine.

“The frontline is everywhere,” the head of MI6, Blaise Metreweli, warned. “The export of chaos is a feature, not a bug, in the Russian approach to international engagement.” It was the product, she said, of Putin’s “aggressive, expansionist and revisionist mindset”. Keir Starmer says western intelligence believes Russia could attack a Nato country within the next four years – which makes the furious row over future UK defence spending all the more relevant.

Anne Keast-Butler, head of Britain’s GCHQ spy agency, claimed last month that Moscow’s forces were “going backwards on the battlefield”. Putin’s response entailed intensifying pressure on Ukraine’s allies and neighbours, notably through cyber-attacks and covert disinformation campaigns. Moscow was “relentlessly targeting critical infrastructure, democratic processes, supply chains and public trust”, she said.

Russia’s offensive is becoming more physically aggressive, too. Armed drone and combat jet incursions into Nato airspace are multiplying. Thousands of GPS interference incidents, disrupting civilian aviation and maritime navigation, are blamed on Russia. Poland’s rail network, which supplies Ukraine, has been sabotaged. Germany and the UK have suffered similar attacks. Baltic undersea pipelines and internet cables have been cut. In this undeclared war, Norway’s land border with Russia, the North Sea and the North Atlantic approaches are emerging fronts.

The expanding battlefield has a strong geopolitical aspect. The EU, having imposed additional sanctions on Russia last week, is finally opening formal membership talks with Ukraine. Next month’s Nato summit will see renewed pledges of solidarity, notwithstanding US backsliding. On Europe’s eastern frontier, most recently in Moldova and Armenia, Russian influence campaigns have been repulsed. Viktor Orbán’s defeat in Hungary was a big setback for Putin and pro-Moscow far-right populist-nationalist forces. The western Balkans are another testing ground.

Russia is expected to further intensify hybrid warfare operations across Europe, the Centre for Democracy & Resilience thinktank said. A key aim is undermining coordinated western action by spreading fear and confusion. At some point soon, it suggested, European states will have to abandon one-off responses, acknowledge they are collectively under attack, and hit back by imposing greater “direct, asymmetric costs” on Russia. Amid the biggest planned rearmament in Europe since the 1930s, it’s but a short step to head-on east-west military conflict.

The more robust the pushback, the more extreme may be Putin’s reaction. His original decision to risk a full-scale invasion of Ukraine was not rational. He has since resorted to grotesque “human wave” infantry assaults, mass child abductions, innumerable war crimes against civilians, reckless attacks on nuclear power plants and “deranged” hypersonic ballistic missile strikes. These are not the actions of a normal, level-headed person. So when ex-president Dmitry Medvedev, Putin’s mouthpiece, threatens Europe with nuclear weapons, as he often does, that ultimate madness cannot be wholly ruled out.

How does this end? Maybe it doesn’t. A third awkward question arising from Putin’s foundering Ukraine campaign concerns the shape of any future “peace” agreement. Ukraine and Europe are aching for it all to stop. Knowing this, Putin may try to freeze the conflict while reorganising and re-arming; or he could accept Zelenskyy’s ceasefire offer without sincerely committing to a lasting settlement. Herein lies great danger for Kyiv. Public pressure to bring the troops home and hold fresh elections could fracture Ukraine’s fragile unity. If the Russian threat appeared to recede, European governments might reduce military support. A ceasefire without cast-iron, pre-agreed security guarantees could render Ukraine more, not less, vulnerable to renewed aggression.

Current western optimism may be misplaced. Yet it helps to remember that one man alone is the primary cause of all this pain and suffering – not history, geography, identity or ideology. The Russian people have a responsibility, to Ukraine, the world and themselves, to remove him from power, as previously argued here. Without Putin, everything is possible. With him, it’s war without end.

• Simon Tisdall is a Guardian foreign affairs commentator