> One theory that explains it is that his objective at this point is to lose - but lose to USA or NATO, not to Ukraine.

Interesting perspective, and it makes sense. There's probably less shame in losing to the most powerful alliance in the world, than losing to a former vassal.

This might actually increase the chance of him using tactical nukes; that's the surefire way to get NATO involved. But ideally he'll want to lose just barely to NATO; he doesn't want to get completely destroyed. That's probably why he's escalating one small step at a time.