Territorial claims are often a tough call. Not that anyone asked me, but I look at it this way. One, is there validity to the claim? And two, is it worth getting the US into a conflict over that claim?
Take Crimea. The Russian claim on that territory is valid enough - in my mind - that it’s not worth getting the US involved. If Turkey or anyone else wants to get involved, that’s their business.
Now take, say, Estonia. As you noted, Estonia was once part of the Russian Empire. But I don’t see a Russian claim to Estonia as valid. For one thing, most people living there are a separate ethnic group.
So if Putin moves on Estonia, I’d take action. Not with tanks (too risky), but with a strong economic blockade, like was done to apartheid South Africa.
[So if Putin moves on Estonia, Id take action. Not with tanks (too risky), but with a strong economic blockade, like was done to apartheid South Africa.]