Why?
Democrats currently have a 30-plus seat majority in the House. It's possible that the Republicans may cut in to that but it is highly unlikely that the they will retake the House. In the Senate it is likely that the Democrats will pick up a couple of seats if not retake the Senate. But even if the Republicans have 50 or 51 seats, with Romney and Murkowski a Republican majority vote on anything is not a guarantee.
With the President on the ticket for 2020 how do you see the turnout vs 2018?