Vladimir Putin made the Budapest Memorandum a dead letter with his first invasion of Ukraine in 2014. But the betrayal of Budapest isn’t forgotten in Kyiv, as President Volodymyr Zelensky noted bitterly in weekend remarks in Munich.

Budapest shows again the folly of trusting parchment promises in a world where autocrats think might makes right. More damaging is the message that nations give up their nuclear arsenals at their peril. That’s the lesson North Korea has learned, and Iran is following the same playbook as it connives to build the bomb even as it promises not to do so.

The inability of the U.S. to enforce its Budapest commitments will also echo in allied capitals that rely on America’s military assurances. Don’t be surprised if Japan or South Korea seek their own nuclear deterrent. If Americans want to know why they should care about Ukraine, nuclear proliferation is one reason. Betrayal has consequences, as the world seems destined to learn again the hard way.