They will almost certainly lose seats in 2018, given the map. The big question is whether or not Republicans can get a filibuster-proof majority.
I honestly can't see the GOP netting eight.
Yeah, not gonna happen with Trump as President. If Dems can hold the net loss to two or three, they should be quite happy.
I don't know. Some analysts think that the GOP could have a supermajority in the Senate in 2018. They can pick up OH, MO, IN, MT, WV, ND.
I don't think Ohio will flip with Trump as President. Trump will also allow Tester, Manchin, and Heithkemp independently without the weight of a Dem President. Donnelly and McCaskill, however, I see as almost sure losers.