Kinda seems like Russia is getting fucked up pretty badly already and they haven't even taken one country. Seems doubtful they would have much luck against an alliance.
If the US leaves that alliance and then starts surreptitiously sending drone parts to Russia, it'll get dicey.
If the AfD forms a coalition government with the normal conservatives and Germany decides to turn inwards and keep Deutsche money für die Deutscher, it'll get dicey.
If Macron finally completes his heel turn and appoints Marine le Pen to interior secretary...
If Italy keeps going the way they've been going...
If the Finnish right decides that joining NATO was a mistake that let too many minorities in...
If the rest of Africa goes along with the Sahel nations and starts funneling their resources into the Russian war machine...
If Modhi lets Russia open more factories in India...
If China decides that they're cool with sharing power on the global scale and fully buys in on the BRICS bloc...
Russia looks weak right now because the invasion has been such and embarrassment, but that can change surprisingly quickly. The global shift towards authoritarianism is coming hand-in-hand with a shift away from US/Eurocentric hegemony.
You vastly underestimate the size and power of the US military. This isn't even a brag; it's atrocious that our military is so large, but the US would have little trouble taking on Europe.
That's what they said about Afghanistan too though. Plus, the odds of the US getting directly involved in a war against Europe any time soon are still pretty damn low.
The US can't project power without aircraft carriers which would be gone quite quickly. Noone has a counter against stealth subs and Europe has both the best and plenty.