“It was extremely, extremely emotional,” said a European official briefed on the call. “He was essentially saying: ‘Look, we are here dying for European ideals.”

Before disconnecting the video call, Zelensky told the gathering matter-of-factly that it might be the last time they saw him alive, according to a senior E.U. official who was present.

Just that quickly, the Ukrainian president’s personal appeal overwhelmed European leaders’ resistance to imposing measures that could drive the Russian economy into a state of near collapse. The result has been a rapid-fire series of developments boosting Ukraine’s fight to hold off the Russian military and shattering long-standing limits on European assertiveness in national security affairs.

The actions culminated on Saturday, when the U.S., Canada, the United Kingdom and the European Union announced they would bar several major Russian banks from the global financial messaging system known as SWIFT, crack down on Russian oligarchs, and prevent the Russian central bank from bailing out the domestic economy. The unprecedented moves led Russians to crowd ATMs in a desperate bid to withdraw cash and sparked a furious response from Putin, who called them “illegitimate” and ordered his nuclear forces to a higher state of alert.