the United States and Russia in the form of the Budapest Memorandum, signed by Bill Clinton, Boris Yeltsin, and John Major, with pledges to “respect the independence and sovereignty and the existing borders of Ukraine” and the “refrain from the threat or use of force against the territorial integrity or political independence of Ukraine.”
Memorandums are non-binding and do not, for example, pass Congress, and certainly are not the 'supreme law of the land' like treaties with mutual self-defense clauses. That memorandum bound the US to nothing and whatever it meant expired with the president who signed it. It is no more surprising that the USA has not invaded Russia over its violation of the memorandum than it is surprising that the USA did not invade Japan in 1905 or 1910 for colonizing Korea despite the letters of assurance to the Korean king and (some interpretations of) the previous treaty. With NATO, everyone understands that an attack on a NATO country will involve American reprisals; in contrast, I've never even heard of this memorandum until the past year where suddenly everyone is invoking it as an example of how hollow American treaties are.
Memorandums have less prominence than treaties so the public relations cost to ignoring them is indeed smaller.
With NATO, everyone understands that an attack on a NATO country will involve American reprisals
Only if President Obama wanted to initiate reprisals, and does everyone know that he would? Yes, he would certainly do something symbolic, but would he take military action against Russia if Russia, say, decided to take back Estonia? I would give it less than a 50% chance. If Ukraine were a NATO member and Russia still did what she did, do you think that the U.S. would have taken military action against Russia?
Some of the comments on the link by James_Miller exactly six months ago provided very specific estimates of how the events might turn out:
James_Miller:
Me:
"Russians intervening militarily" could be anything from posturing to weapon shipments to a surgical strike to a Czechoslovakia-style tank-roll or Afghanistan invasion. My guess that the odds of the latter is below 5%.
A bet between James_Miller and solipsist:
I will bet you $20 U.S. (mine) vs $100 (yours) that Russian tanks will be involved in combat in the Ukraine within 60 days. So in 60 days I will pay you $20 if I lose the bet, but you pay me $100 if I win.
While it is hard to do any meaningful calibration based on a single event, there must be lessons to learn from it. Given that Russian armored columns are said to capture key Ukrainian towns today, the first part of James_Miller's prediction has come true, even if it took 3 times longer than he estimated.
Note that even the most pessimistic person in that conversation (James) was probably too optimistic. My estimate of 5% appears way too low in retrospect, and I would probably bump it to 50% for a similar event in the future.
Now, given that the first prediction came true, how would one reevaluate the odds of the two further escalations he listed? I still feel that there is no way there will be a "conventional battle" between Russia and NATO, but having just been proven wrong makes me doubt my assumptions. If anything, maybe I should give more weight to what James_Miller (or at least Dan Carlin) has to say on the issue. And if I had any skin in the game, I would probably be even more cautious.