The writing is on the wall. The Democratic base is hugely excited -- largely due to their distaste for Trump. The Republican base -- at least for most of 2017 -- has been less passionate. And that sort of base enthusiasm disparity has translated -- and likely will continue to translate -- into major gains for Democrats in the midterms.
History suggests that Republicans are in a familiar position: Standing in the shallow water watching a massive wave building out in the ocean. According to Gallup, the average seat loss for the president's party in midterm elections with a president under 50% approval (as Trump is now) is 36 -- a number that, if past predicted present, would cost Republicans their House majority.