The invasion of Ukraine has polarized members of Russia’s elite, many of whom view it as reckless. Real sanctions, such as blocking access to their plush London apartments, will show that Mr. Putin’s folly comes with serious costs.

Second, Western authorities must investigate ill-gotten gains from Russia within their jurisdictions. The Anti-Corruption Foundation, which I established in 2011, has revealed dozens of major cases of graft. In 90 percent of those cases, Russian money was laundered in the West. Sadly, American, European Union and British law enforcement agencies have stymied our efforts to investigate such criminal plunder.

“Crimea has always been an integral part of Russia in the hearts and minds of people,” Mr. Putin claimed this week. But even among the most nationalist and pro-Soviet of our people, a longing to restore Crimea to Russian rule faded years ago.

Yet Mr. Putin has cynically raised nationalist fervor to a fever pitch; imperialist annexation is a strategic choice to bolster his regime’s survival. Mobilizing the masses by distracting them from real problems like corruption and economic stagnation can take place only beneath the banner of fighting external enemies.

What is truly alarming in Mr. Putin’s rash behavior is that he is motivated by the desire for revenge against the Ukrainian people for revolting against a Kremlin-friendly government. A rational actor would know that the precedent of holding a local referendum to determine sovereignty is risky for Russia — a federation of more than 80 disparate regions, including more than 160 ethnic groups and at least 100 languages.

It is true that the consensus in both Russia and Crimea is that the peninsula has historically been closer to Moscow than to Kiev. But the notion that this reunification should be achieved at the end of the barrel of a gun is supported only by Mr. Putin’s hard-core base. The opposition has spoken clearly. The antiwar protest held in Moscow over the weekend was the largest in two years, and it exceeded any counterdemonstration mustered by pro-Kremlin movements.

There is a common delusion among the international community that although Mr. Putin is corrupt, his leadership is necessary because his regime subdues the dark, nationalist forces that otherwise would seize power in Russia. The West should admit that it, too, has underestimated Mr. Putin’s malign intent. It is time to end the dangerous delusion that enables him.