[aguaviva]

You can even go back to the 90s and promises that NATO made that it would not expand to eastern Europe

And I encourage you to do so, because if you look at the actual event protocol it simply doesn't support what you're saying.

The bottom line is that whatever was said verbally at the time was understood by all participants to be part of the brainstorming process in the course of negotiations of what would eventually become the 2+4 Agreement. And simply put, this particular proposal did not make it into the agreement. As one notable observer put it: "It was tough, everyone knew that only what is written in black and white in the contract counts."

That's why Gorbachev insists (in an interview you can easily find) that even though he felt that NATO expansion was against the "spirit" of the negotiations, there were no statements about NATO expansion that rose to the level of a "promise". We also have Shevardnadze's equally stringent denial (per the sibling commenter), and strong counterweighing factors, such as Russia's greenlighting of the first round of ascensions (PL, CZ, HU) in the 1997 CFE Treaty, which by itself renders the "broken promise" theory unequivocally moot. And some notable language in the NATO-Russia Founding Act signed in the same year as well.

The war was at least partly instigated by our refusal to promise to keep Ukraine neutral and out of NATO.

That's a severe misreading of the article you cite in association with this statement. Simply put, that's not the language of the article, and that's not an implication it makes.

How would you feel about Russia making trade deals with Mexico, sponsoring pro-Russia politicians,

So far so good. Whatever one may feel about Mexico taking that direction -- it is after all a sovereign state. And while such circumstances would certainly be a matter of concern to the US, the idea that they amount to something in response to which the US would need to launch a full-scale invasion of Mexico (or that such a move could possibly be beneficial the US in any way) would, of course, be seen as batshit insane.

... and selling advanced military gear to them?, ... How would you feel if Mexico was attacking us with cruise missiles supplied and operated by Russia?

If this happened only after the US launched an invasion of Mexico as plainly stupid and unprovoked as Putin's invasion of Ukraine -- all rational observers would agree that Mexico would of course have a perfect right to defend itself -- indeed, "by any means necessary".

Including the procurement of advanced military gear of virtually any conventional description, from whichever source it could find.