The logistics for the Senate are extremely tough for Dems in '18 - even if there is broad anti-Trump sentiment. It's just a great year for the GOP because of where the contested seats will be.
I don't think the Dems will pick up any seats there (they will in the House). If they lose 1-2 seats, it would actually be pretty positive for them given the landscape.
So, Trump will get another year after '18 at least. Since the GOP has now set the precedent that there will be no appointments in the final year of a Presidency, we'll see how it holds after that.
