awooga83 — I think it depends who you’re referencing on the Eastern front.
Poland being invaded would certainly trigger a response - partly because they’ve invested enough in their defenses/army that they wouldn’t need as much support. NATO as an organization, and its countries individually, would be far more bullish on a positive outcome which in turn makes support easier to sell and more compelling on the backside.
I do fully agree with you though that the Baltic countries may not be afforded that same support. An invasion of those countries would require NATO fighting back by forcibly attacking within Russia which is a far greater step than supporting defensive operations.
Hungary is another possible inflection point. Russia’s “invasion” there would more likely be via political influence, and softer actions, but would how would NATO (and the EU) respond to that tampering and potentially internal encouragement?
