US is on another continent. It doesn't needs that buffer, Atlantic ocean is rather wide and deep.
You seems to ignore what Ukrainians want. NATO is an open alliance (open https://www.nato.int/ and read what they wrote there), not an American empire.
> We then openly backed the 2014 putsch in Kiev
That backing was limited to verbal expressions of support. Technically you're not wrong and this might count as "backing", but I don't believe that changed anything at all in the outcome.
WARNING: Troll factory catchphrase ["putsch"].
NATO is an excuse for America to have their colonising army in Europe while making it look like something else. America can brainwash Europeans by using the media of these compromised nations and their own peasants via their corrupt corporate media... but don't expect outsiders, include Russia, to fall for this nonsense.
NATO proposed Ukrainian and Georgian membership of NATO in 2005-2008, in the clear knowledge that this would destabilize the situation.
France, Germany, and others were against this. The proposal began the issue. https://www.youtube.com/watch?v=SJBQikfYyKs
We then openly backed the 2014 putsch in Kiev, an open act of aggression just as irresponsible as a military incursion. CIA John Brennan, Senator John McCain, and Diplomat Victoria Nuland were there in Ukraine when Yanukovych was being overthrown. There is also evidence to show that we were involved through NGOs in overthrowing and promoting an atmosphere desiring the overthrow of Yanukovych.