Polarization isn't the "end all, be all", but it has certainly made it more difficult for Democrats and Republicans alike to win on territory hostile to their party.
There are several Democratic governors from red states and Republican governors from blue states. The only thing we know for sure is that it’s virtually impossible for a Republican to win a federal race in a Democratic state barring some very special circumstances like a low-turnout special election (and even then, MA-SEN 2010 is really the only example here), but that’s been the case since at least 2004. "Polarization" is hardly a recent phenomenon.
Just look at the three Democratic Senators in strong Trump states who were defeated last year, in that same "wave" environment.
Two of these Democratic Senators were incredibly unpopular (McCaskill) or ran hilariously bad campaigns (Heitkamp) and
still outperformed Clinton by a lot (and certainly by way more than they should have). I agree that Donnelly was probably always destined to lose, but keep in mind that a Democrat actually won a federal race in a Trump +42 state and Democrats were successful in defending several Trump states, including Republican-leaning MT and OH.
And I've made clear that I believe Edwards will win reelection, but he will do worse than in 2015.
That remains to be seen. JBE definitely benefits from the the fact that his reelection race is an off-year election and no unpopular Democrat is in the White House. Even Hogan did better last year than in 2014 despite the national environment being the exact opposite of 2014. Popular incumbent governors generally don’t lose reelection.
Abraham is not a strong opponent, but he doesn't have the same kind of ethical or political baggage that Vitter did. And Mississippi is notorious for its racial polarization, and a gubernatorial race is quite different from an AG one.
Agreed on Vitter (although I remember people here arguing that Vitter was a shoo-in because of "polarization", "inelastic Deep South" and "Obama" back in 2015, so these arguments aren’t even new), but MS has always been polarized, even when Hood kept winning by a landslide in his AG races. He clearly has a lot of crossover appeal, and the Democratic floor in MS is extremely high.