The US would not go to war over Estonia...
Aside form the fact that it would immediately render NATO meaningless - which in itself would constitute one of most significant paradigm shifts in international politics and the balance of power since the end of WWII - it would also completely obliterate the credibility of American foreign policy for the next 50 years or so. Why would anyone ever see an advantage in entering a military alliance with the US again?
I'm so bold to say that such an event would be identified by future historians as
the turning point at which the United States ceased to be a superpower (and perhaps a great power too) and the "Asian Century" began.
All of this is purely academic though. Exactly for the reasons I just mentioned, the United States would of course go to war over Estonia. (And as long as Putin is convinced that the U.S. would, he probably won't touch Estonia.)
