political forecast for Nov 2018

It's possible that the Dems would over-play their hand on Trump or some aspect of identity politics like this-- to the point of causing electoral trouble. But probably not. 

 

Even so, assuming the economy is still strong... (This is to be expected given the business cycle-- post-Bush/early-Obama/Congress/Fed trying to manipulate it-- and perhaps heightened a bit by tax reform and some deregulation.) They should expect, at most, modest gains in 2018.