The idea that 2018 can be a good year is ludricious. Democrats will lose senate seats on that year's map (their only real pickup opportunity is NV, they probably won't have enough money to contest AZ with all the seats they have to defend.) - the question is simply how many. The states in green on the map below are democratic seats up in 2018 that are something less than Safe D at this very early stage:
Minnesota? Klobuchar is completely safe. Even Dayton and Franken just won easily in a GOP tsunami, and they're nowhere near as popular as Klobuchar is.
NM/CT/WA are also stretches, but yeah, that still leaves ten vulnerable Dem seats compared to two vulnerable Republican seats. I think the OP was referring more to the House/governorships, but I don't see how regaining one half of Congress and some governorships is worth tons of far right legislation and Scalia-clone SCOTUS picks.