It all depends on circumstances. After Russian rebellion in Narva, Estonian government will have a choice -
1) Stop discrimination of the Russians and give them equal political rights.
2) Use military force to attack Narva.
If they chose latter Russia will have a choice:
1) Allow Estonians to genocide the Russians.
2) Attack Estonia, NATO or not NATO.
If they choose latter, the USA have a choice:
1) Allow Russia to eliminate Estonia
2) Fight a nuclear war to eliminate Russia.
And, as the USA do not possess the credible first strike capability, and can't attack Russia and do not suffer unacceptable damage after it, it's highly unlikely, that the USA will commit suicide.