"UN Security Council action" is a broad term that can include deployment of international UN-led military forces, as in the Korean War: https://en.wikipedia.org/wiki/United_Nations_Command
A few years prior to the Budapest Memorandum, the UN Security Council had authorized military action to liberate Kuwait. 42 countries participated in the coalition that drove Iraqi forces out of Kuwait: https://en.wikipedia.org/wiki/Coalition_of_the_Gulf_War
The expectation at the time was clearly more than just "we'll bring it up at the UN for dicussion". The current weaseling over the exact wording looks weak and pathetic, and has a certain flavor of propaganda that tries to convince everyone of something that's not quite true. The fact remains that the US strong-armed Ukraine out of nuclear weapons, and when Ukraine was eventually invaded, tried to strong-arm Ukraine into surrender. This reflects very poorly on the US.
"Russia blocks Security Council action on Ukraine"
...
"A ‘no’ vote from any one of the five permanent members of the Council stops action on any measure put before it. The body’s permanent members are: China, France, Russian Federation, the United Kingdom, and the United States."
https://news.un.org/en/story/2022/02/1112802
(emphasis mine)
This is 101-level UN stuff. If Ukrainian diplomats were unaware that Russia can veto Security Council resolutions, that means they were totally incompetent.
It's also misleading to say the US "strong-armed" Ukraine out of its nukes... it was originally Ukraine's idea to abandon nukes, and they didn't have the control codes for the nukes on their territory anyways. The US attempted influence via carrots (financial assistance), not sticks ("strong-arming").
In any case, we did far more than just bring it up at the UN for discussion. See this map from a year or two ago: https://pbs.twimg.com/media/HKNCFWPbEAA7p5g?format=jpg&name=...
Mostly, in response to US generosity, Europeans just complained that the US should give even more. Your comment illustrates this perfectly--you speak as though the US only responded via UN diplomacy, completely neglecting over one hundred billion dollars the US sent in Ukraine aid, to a country which is not even a treaty ally of ours. When Biden was president, right after he saved Ukraine's butt in the initial invasion, public opinion of the US in Europe was barely even net-positive.
The real question is why Europeans spend so much time harassing the US for Ukraine funds, and so little time harassing tight-fisted countries which are actually in Europe like Ireland, Switzerland, Austria, Spain, etc. The answer: Europe has a transatlantic philosophy that the US brings the guns and the Europeans bring the scolding. As long as Ireland/Switzerland/Austria/Spain nod along with the scolding, they are doing their part, as far as Europe is concerned.
It is safe to say that the present lack of leadership from the US was not foreseen at the time. It was unimaginable that Russia would launch a major ground war in Europe and that the American president would blame the victim of the aggression and try to coerce them into surrender while sucking up to the aggressor. This is not how things were conducted back then. It was the era of Schwarzkopfs showing strength and resolve by giving presentations on how coalition tanks had pummeled the enemy in the past few weeks, not of Sullivans showing weakness and indecisiveness by endlessly yapping about "escalation".
The core problem is that the US has spent almost a century embedding itself in all kinds of relationships (cultural, political, economic, military), but has lost the ability to carry out that central role. Biden did not save Ukraine. The limited but valuable military support fostered an unhealthy relationship that gave the US a veto over Ukraine's (and other allies') actions, but the US leaders do not have the statemanship to use that power responsibly. Biden's legacy is the shortsighted micromanagement that turned the fast and effective Ukrainian counteroffensives of 2022 into slow and costly trench warfare of 2026, all while emboldening enemies like Iran to launch assaults like October 7th.
The Budapest Memorandum only requires going to the Security Council if nuclear weapons are involved. There's no required action at all for non-nuclear attacks. This isn't "weaseling over the exact wording," it's just the plain language of the memorandum.
It really amazes me how much misinformation is out there about this thing. It only has six points, each one a single paragraph long. It's very quick and easy to read, yet people apparently can't be bothered to look up the actual text of the thing they're discussing.
You can argue all day about the letter versus the spirit of the Budapest memorandum, but good luck getting any other countries to give up their nukes in the future.
That's only one consequence of Trump's de-facto betrayal of Ukraine in support of his daddy figure in the Kremlin.
I have a really hard time accepting the idea that the spirit of the memorandum was that the signatories should actively defend Ukraine against non-nuclear attack, when it would have been so easy to write that explicitly.
I completely agree about no countries giving up their nukes in the future, but that's a consequence of the weak agreement, plus other actions like knocking over Iraq and Libya but not North Korea, tearing up the JCPOA with Iran, and... well, it seems like non-proliferation is mostly lip service in general.