America will do nothing except 'strongly condemn' what's happening, just like the rest of the world. The simple fact is that there is no real upside to risking actual war with Russia - that the Russians will dominate the Ukraine while walking away with a bloody nose (in the form of minor troop losses of its own) is a foregone conclusion. Without more, that's a localised conflict that Russia rather hilariously can try to claim the moral high ground about (NATO encroachment, historical alliances, American instability and foreign meddling), but if America or indeed any of the other nuclear powers gets involved, the risks increase massively very quickly. If two nuclear powers went at it properly here - I don't care which two - we enter into long-tailed territory and it's something we've simply never seen. There's absolutely no chance America or the UK risk that - they can get their wheat from somewhere else.
On the one hand, I feel bad for Ukrainians. On the other hand, the whole world saw it coming, just like we can see China invading Taiwan at some point in the future, and the calculus will be the exact same: Taiwan means more to China than it does to America, and the Ukraine means more to Russia than it does to the West.
It is perilous to fight somebody, whether it's Putin or Xi, with vested emotional interests in the subject matter of the fight when all you've got is ideology.
And so nothing will come of this except 'strong condemnations'. As if any strongman ever gave a fuck.