I imagine the Democrats will pick up a number of "solid R" open seats just because that's really been the norm for midterms for the party that doesn't hold the White House. Governor races really don't follow partisan lines like both the Senate/President do.
If so - another scenatio is also possible: expected Trump blunders will not seriously affect governor elections with their own dynamics. In such case Democrats will NOT "pick a number of "solid R" open seats"
Not very likely. Even 2002, which was otherwise a good R year, the Republicans lost a good number of governor seats simply because Bush was in the White House (They did gain some in the deep south though).
Governor seats going the opposite way of the White House has almost become a norm in the country.
