I'd like to hear a supporting argument for that contention.
the idea that the USA has an interest in defending Bulgaria from anyone, at any time is ludicrous to me.
Romania?
And, would you expand NATO to Ukraine and Georgia...and would their defense with US Forces make sense?
To "make sense" there would have to be a real US strategic interest.
So I ask you, do you think defending the original NATO countries make sense?
If so then why wouldn't Estonia make sense?