Just winning the House would not be enough to make Democrats complacent.
Problem is, The Deplorables will wake up just as Obama's base did and might be powerful enough to make 2020 another 2012.
Obama's base gave him two commanding and decisive victories. Trump's base got him a thin victory against the second most unpopular candidate of all time. They're not the same.
This is very true. Trump's victory was either the most shrewd example of political calculation in history (coupled with Hillary's indefensible failure to campaign in WI and MI) or the dumbest of dumb luck. Given how Trump consistently seems to outsmart his enemies just when they they they have him, I'll vote the former, granting that pulling that off in 2020 will not be easy.
The complacency Democrats will have will manifest itself in the belief that they can entertain snarkfests and feuds within their own ranks. They need to get behind the candidate that will be able to gain the broadest base of support and run a campaign fixed on income inequality, because Trump, on the issues, is surprisingly strong. The income inequality issue will resonate, however. In truth, the identity politics will olay itself out on its own; Trump's not going to gain any new minority support and women are pretty much aware of what Trump is about, one way or the other.