None. There is no state that is unwinnable for either major party at the gubernatorial level. If California Or Maryland can have a Republican Governor than Republicans can win anywhere, and if Doug Jones can win in Alabama (in a senate election no less) than Democrats can win anywhere. Governor elections are just naturally less polarized and can more easily attract moderate candidates from the opposing party that have strong bipartisan appeal.
California hasn’t elected a Republican governor since 2006, which is an eternity in politics. Also, there are several Republican states with more unfavorable demographics for Democrats than AL, which at least has a solid black and urban base (and to a lesser extent favorable suburban trends) for Democrats to build upon. Just because Democrats (narrowly) won a
special election in Alabama doesn’t mean that they can realistically expect to win ND and AR in a regular year.
You have a point about Hogan, but I’d argue there are Democratic states which have a more unpersuadable and radicalized Democratic electorate which isn’t going to consider voting for any Republican under any circumstances.
