We ratified the UN Nuclear NonProliferation Treaty. The Budapest thing was an accession to that ratified treaty, following accession protocols that the senate ratified.
“It refers to assurances, but it does not impose a legal obligation of military assistance on its parties.[1][27] According to Stephen MacFarlane, a professor of international relations, “It gives signatories justification if they take action, but it does not force anyone to act in Ukraine.”[26] In the US, neither the George H. W. Bush administration nor the Clinton administration was prepared to give a military commitment to Ukraine, and they did not believe the US Senate would ratify an international treaty and so the memorandum was adopted in more limited terms.[27] The memorandum has a requirement of consultation among the parties “in the event a situation arises that raises a question concerning the ... commitments” set out in the memorandum.[28] Whether or not the memorandum sets out legal obligations, the difficulties that Ukraine has encountered since early 2014 may cast doubt on the credibility of future security assurances that are offered in exchange for nonproliferation commitments.[29] Regardless, the United States publicly maintains that “the Memorandum is not legally binding”, calling it a “political commitment”.[30]”
https://en.wikipedia.org/wiki/Budapest_Memorandum_on_Security_Assurances