It seems likely that Putin could take Ukraine without undue difficulty if he put his mind to it. Why doesn’t he? There are several possible explanations, most of which are not mutually exclusive:
- The existing American and EU sanctions trouble him more than he lets on, and he is concerned about new ones;
- His military hasn’t performed all that well in Ukraine up to now;
- He fears the cost of occupation, which would undoubtedly include terrorist attacks within Russia’s boundaries;
- He didn’t want to embarrass his ally Trump while he was still in office; and
- Ukraine, for him, is not the end game–it is a piece of a larger puzzle, involving domestic politics, the destruction of the EU, and the elimination of the US as a serious threat. Having an ongoing, unresolved struggle with Ukraine actually helps him more than a military victory and an occupation.
I suspect it is all of these. Don’t be surprised if Ukraine becomes a flash point again in the near future, particularly if #4 is part of the equation.