Op-ed by Alyona Getmanchuk, Director of the New Europe Center, for Financial Times.

“How it is it possible? . . . In the 21st century? . . .  In Europe?” These are the questions echoing in Ukraine, voiced by people from all walks of life. Ukrainians are watching with horror and dismay as Vladimir Putin outwits the democratic world yet again and it seems nobody has the nerve to stop him.

The Russian president is so confident that he hasn’t even bothered to upgrade his old playbook: he is using the same hybrid tactics he has in the past: moving Russian troops into another country’s territory under the false pretext of defending Russian-speaking people or those to whom he has granted Russian citizenship.

This ploy is so tired that there’s a joke in Ukraine about a formerly Russian-speaking man who suddenly starts speaking in Ukrainian. When asked why he switched, he replies: “I don’t want Putin to come to defend me”.

By pretending to be a peacekeeper in the Donbas region, and formally recognising the Moscow-backed separatist “republics” of Luhansk and Donetsk, Putin has once again proven himself a war-monger. There is no doubt in the minds of Ukrainians that his imperialistic agenda will not be satisfied by this incursion. Otherwise, why would he have massed up to 190,000 troops at the Ukrainian border?

The reaction from western countries this week is strong by the standards of 2014 — but not by those of 2022. The wave of sanctions announced by the US and Europe on Tuesday is a good first step, but world leaders should make ready to roll out more of them before waiting for a full-scale invasion. Western leaders must now do what they have been reluctant to do for the past eight years, and choose deterrence rather than more dialogue. It was clear from the very beginning that Putin would start any new invasion in a manner that could allow him to dodge sanctions for as long as possible.

US President Joe Biden in particular should been feeling a strong sense of déjà vu now: he is the only western leader who not only witnessed, but had to deal directly with Putin’s aggression in 2014 at the top of government. If anyone should be drawing lessons from that time, it is him.

He deserves credit for his efforts to align the US and its European partners’ responses and for increased military assistance to Ukraine. He must now put in place the full force of sanctions available to him and give the green light to an upgraded version of the Ukrainian Democracy Defense Lend-Lease programme that would boost the provision of military equipment.

Both Ukraine and the west have had enough time to draw lessons from the 2014 annexation of Crimea and, accordingly, to prepare for Putin’s next offensive. Some useful actions were taken, but even the most important of these has been blurred by the mixed messages western nations have sent to the Kremlin. The long prevarication over the Nord Stream-2 project, the calls from different world capitals to ease sanctions, the attempts by international leaders to establish dialogue with Putin — all these did nothing to deter him.

Western leaders have failed to accept a simple fact: today Russia poses an external security threat, but it is also a source of domestic destabilisation — not only to Ukraine, but to the US and many other western countries, too. Putin has convinced the world he is ready to start a war in Ukraine, but, as of now, the west has failed to convince him that the price of his aggression would be higher that the potential gains. As Ukraine imposes a state of national emergency, it is already paying the price for that failure. According to the most recent estimates by the Ukrainian government, the country is losing $3bn a month as a result of the current escalation.

It is not late to prevent what could be the bloodiest conflict in Europe since the second world war. I find it impossible to believe that the combined efforts of democratic leaders are not enough to counter a single authoritarian, who has been successfully outwitting the democratic world for more than a decade.

Unless Putin is stopped now he will continue to do this for years — and each time his imperialist plans will grow grander and more catastrophic.