The US military is not an unlimited resource, I would rather they deter this....
The role the US has in NATO against Russia is :
- nuclear umbrella (yes, there are two other nuclear powers in NATO but both have small stockpiles amd one relies on US tech)
- air force (no other NATO army relies so heavily on air superiority in its doctrine and has the planes to back it up.)
- intelligence (no other NATO country has that huge a spy network, sattelites and intelligence sharing)
Only after that comes the army. The European armies are big enough and even better equipped with artillery and tanks. It is more an issue to get everyone to work together if whatever is not a common NATO mission (which thus must include the US ) and ground forces need to be backed up by air forces (which is hard to provide without the US). The NATO command structure has also a lot of US personnal embedded, making it a pita to work without.
The branches of the US military NATO would need the least against Russia is the US Navy and the US Marines. NATO has so many other navies and controlls nearly all the relevant ports. Europe alone could easily blockade Kaliningrad and St.Petersburg, Turkey could easily control the Bosporus and then then it is over for the Russian navy.
But the main NATO problem is that if the US stops providing reliable backing, what will the other nations do ? Whithout the US they can't counter Russian nukes and if the strongest country is allowed to renege on the allience, others (who are far away from the action or particularly scared by the nukes or currently have a Russian friendly gouvernment) might back out as well.
The US always made sure it retains the leadership position in NATO (and sabotaged common European defense initiatives). By withdrawing during a crisis the NATO therefore becomes leaderless. And i probably don't have to explain you how this is an issue.