The problem with politics is that negative isn't simply the inverse of positive when it comes to influence. Trump certainly didn't help the GOP get its majority, but now that he's the GOP's guy, his negatives will affect the rest of the GOP and he could very well cost the GOP its majority in the 2018 midterms. If that happens, impeachment most certainly beckons.
That is true, his negatives could tarnish the brand (further). But AC specifically said we could/would lose
because he broke his promises. My (not well made) point was that broken promises isn't going to lose the HR. The people who voted for him were:
1) Going to vote GOP anyway, and will continue to do so.
2) Dems and Independents who voted for him due to his promises.
3) Dems and Independents and GOP who voted for him for other reasons (for example, Hillary).
4) GOP voters who care so much about his promises that they'll punish the party if he breaks them.
5) GOP voters who care about his promises, but won't punish the party if he breaks them.
[hopefully I got that right]
So, if he breaks his promises, we lose some/most of #2, but then we had a decent majority without them anyway and they may have voted Trump at the top and Dem down-ticket, and #4 who I suspect are nowhere near populous to lose us even one seat, let alone 30.