With an end to the war largely on Russia’s terms, as the Trump administration’s actions and statements seem to suggest is in the offing, Putin could claim victory. Conquest by force would be rewarded. An empowered Russia would expand again—on top of its previous occupations and annexations of parts of Moldova, Georgia, and Ukraine after the 2014 invasion. That would send a message to all Russians that, despite their hardships, their leader has brought their country back to the path of glory and global power, teaching rebellious Eastern and Central Europeans a lesson, putting Western Europeans on notice, and leveling the playing field with China, instead of becoming its junior partner. Putin’s gamble would have played off.

There is no conceivable scenario where this experience would not encourage Putin and his circle to double down on imperialism and territorial expansion by force. Defeat—to be kicked out of Ukraine—might lead to a moment of soul-searching in Russia, weaken Putin’s rule, and open the possibility of change. Victory will put more wind in Putin’s sails and provide him with greater resources for his next steps. Should he get control of all of Ukraine, he will control a vast defense industry, military, and population to deploy against new targets.

For Europe, the risk of a military confrontation is rising steeply. As Putin has made clear in his two draft treaties to the United States and NATO, his goal is for Russia to regain the position of the Soviet Union of his youth: control over Eastern Europe, most of Central Europe, and at least parts of Southeastern Europe—and, as a consequence, dominance in a Europe that has been largely abandoned by the United States.

Russian success in Ukraine does not only mean that Putin would soon try do whatever it takes to get the rest of Ukraine under his control. He also has his sights on Moldova and Georgia, the latter of which is already dominated by a Russia-friendly regime. Next, he would wait for the right moment to attack a NATO country using conventional, hybrid, or other methods and move ahead with regime change and occupation. The primary goal would be to demonstrate that it’s each country for itself—that Western solidarity, as expressed in NATO’s Article 5 and the European Union’s mutual defense clause, are fantasies without foundations.

European leaders had the chance to frustrate Russia’s imperial ambitions early on and cheaply, since it was highly capable Ukrainians doing the actual fighting. All that was required was the fortitude to overcome habitual lethargy and overblown fears—and to realize that this was a unique opportunity to show Russia that wars of aggression and conquest remain taboo in Europe. They were warned, and they failed. The risks of acting then were far lower than the risks they face now. And the money they could have invested in their own security by way of supporting Ukraine is small change compared to what it will now take to mobilize their militaries, industries, and societies to secure their borders against a far more belligerent Russia in the coming years.