[T]he United States publicly maintains that "the Memorandum is not legally binding", calling it a "political commitment".
Furthermore, the memorandum states quite clearly:
[The United States as a party to this agreement shall] "[s]eek immediate Security Council action to provide assistance to... Ukraine if they 'should become a victim of an act of aggression'..."
The United States has reportedly done exactly that, and has therefore fulfilled the specific requirements of the agreement. Military intervention by an individual party, to enforce or punish violations of the agreement by other parties, is nowhere required or even contemplated...
;>)
“Barry Kellman, a professor of law and director of the International Weapons Control Center at DePaul University’s College of Law, told Radio Free Europe in 2014 that, “It is binding in international law, but that doesn’t mean it has any means of enforcement.”
He added that there are numerous other treaties that oblige Russia to respect Ukraine’s territorial integrity, including the U.N. Charter and the Conference on Security and Co-operation in Europe (CSCE) treaty.
Evil Putin mocked international law when Harvard University Research Associate Mariana Budjeryn when Russia “glibly” violated the agreement, and did not even attend a meeting of the signatories held in Paris after Russia’s annexation of Crimea in 2014.
She added that some Ukrainians did express regret for giving up their nuclear weapons:
There certainly is a good measure of regret, and some of it is poorly informed. It would have cost Ukraine quite a bit, both economically and in terms of international political repercussions, to hold on to these arms. So it would not have been an easy decision.
But in the public sphere these more simple narratives take hold. The narrative in Ukraine, publicly is: We had the world’s third-largest nuclear arsenal, we gave it up for this signed piece of paper, and look what happened.
And it really doesn’t look good for the international non-proliferation regime. Because if you have a country that disarms and then becomes a target of such a threat and a victim of such a threat at the hands of a nuclear-armed country, it just sends a really wrong signal to other countries that might want to pursue nuclear weapons.
It is indeed correct that Ukraine held nuclear arms after the collapse of the Soviet Union, and then gave them up in exchange for security assurances — assurances that were violated later.”