You'd be right if he used nukes. But I think a limited well-signaled conventional military strike under Article 51 would unify many corners of the world WITH Russia not against.
Most countries in the world secretly resent the USA but play along with them because they know who has the power. Once BRICS showed up and Russia-China relations warmed, we started to see many nations that seemed like Western allies turn away from strict allegence to the West, either to hedge their bets and play both sides, or to join the other side economically, or policy wise, or sometimes even militarily.
Negotiation is the best path if all sides want it. Maybe some European countries want to negotiate. Does the UK? Does the US? Does Ukraine? Are they signalling this by launching ATACMS and Storm Shadows deeper into Russia?
Agree with some of your thinking - still think a strike on US soil is a bridge too far - may just be hopeful thinking. the quasi-axis of US- UK-Ukraine seem to feel the heat of the incoming admin and are like - WTF, if we just escalate the fuck out of it the Trump admin will have to clean up, even if they want to negotiate… the darker side takes that to the extreme with Biden out of it and his cabal going out scorched earth.
Just think a strike on US regardless would unleash the hawks rather than send us to the negotiating table.