Those 3 states at the end are a good place to stop too. With the way white voters are tipped to the Republicans in the other Southern states that lack true metro areas (MS, AL, TN, etc..), there's basically no way to win those states anymore. Any left-wing social position would sink you instantly. Those 3 states have a good shot of getting taken over by their populous cities though (and hipsters in the case of NC).
I'm not convinced that we'd go for the nukes over a smaller country like Estonia. Certainly for a larger ally, but I think if pushed, we balk on smaller invasions and go conventional. And even then, I don't think we use ground troops as much as we use constant drone strikes; it's one thing to hide from drones when you're a lowkey terrorist cell that can move covertly. It's another thing to maintain stuff like an airfield in broad daylight without us obliterating the runways. It'd take about a month for us to drone strike most of the major airfields, and also their aircraft carriers (they've only got the one good one if it's been completed, the other one is ancient and gets tugged back to harbor frequently).
It's been a long time since we had to fight a conventional war against a nation with organization and infrastructure to blow up. Those targets are super exposed and really easy to destroy. If Russia tried to go that route, I give it a few months before top gov't officials "slip in the shower" and the new officials call the whole thing off.