The forgotten men and women

There's been a lot of discussion of people who shifted from voting from Obama in 2012 to Trump in 2016 and some discussion of people who switched from Romney to Clinton.  But there's another group who hasn't gotten much attention--those who switched from Romney or Obama to a minor candidate or write-in.  The share of the vote in 2012 and 2016:

                           2012           2016
Republican         47.2%         45.9%
Democrat           51.0%         47.2%

Libertarian         1.0%           3.3%
Green                 0,4%           1.1%
McMullin           0                 0.5%
Write-in             0.2%           0.8%
Others                0.3%           0.3%

I expect that most of the gain for the Libertarian (Gary Johnson in both years), Evan McMullin, and the write-ins came from people who would normally vote Republican.  Their combined total went from 1.2% in 2012 to 4.6% in 2016, for a gain of 3.4%.   It seems likely that those people are committed voters--otherwise they wouldn't have gone to the polls or would have left the Presidential race blank.  So what they do in 2018 could make a significant difference.  The question is whether they are mostly people who simply would not vote for a Democrat, or people who might vote for a Democrat but not Hillary Clinton, and I haven't seen anything that sheds any light on that.  However, my impression from other data is that negative partisanship has become a strong force.   That suggests that some Republicans who now say that they will vote Democratic this time will switch back at the last minute, and the Democratic gain will be on the smaller side of what has been predicted, giving the Democrats a majority of maybe 225-210 in the House.  But given that Trump has been so prominent in the election, that he's focused exclusively on his "base," and that the base was not that big to start with (a lower share of the vote than Mitt Romney), I'll put the probability of a Democratic majority at over 90%.