ME Sarotte thinks Putin has bought into the concept of a 30-year-old betrayal of a commitment by a past US President to a past Russian President to not expand NATO east to include nations that used to be under Soviet domination. Sarotte says that’s the basis for Putin’s current brinkmanship; he’s merely trying to redress that betrayal, as NATO has, indeed, accepted erstwhile Soviet-dominated (even occupied) nations into NATO.
I think it’s hard to take seriously Sarotte’s view. More likely, it seems to me, is that Putin merely is putting that out as a public rationale. The most likely case for his seeming brinkmanship is that Putin doesn’t see his behavior as brinkmanship at all. On the contrary, he’s convinced—rightly or wrongly—that Biden-Harris will fold in the moment of truth.