Democrats control the house 435-0. Not even NE-3 is free from the purge.
This, and Claire McCaskill wins every county in MO by at least 20 points and then the presidency in 2020 in 538-0 landslide. Even Barrasso is swept away on election day.
Oh, you wanted a serious answer? I doubt this will hurt the GOP much unless it is passed in the Senate without any major changes to the bill. I know this forum has already decided that 2018 will be a reverse 2010 (or worse) for Republicans, though.
Edit: Like windjammer said, if this debate is dragged on forever, it could weaken House Republicans in Clinton districts, but there are 18 months left until election day, so yeah...
It won't be the defining issue of the election unless it actually becomes law, but Cap and Trade did have a measurable effect on 2010 even though it only passed the House. Probably cost the Dems 10ish Appalachian seats that wouldn't have defected over Obamacare alone.
Basically, Dems need to either win back a bunch of working class areas concerned about losing health coverage or find a way to get another 5 point swing out of the Southern suburbs (if tax reform fails, that will help their cause).
I do think that MT-AL just became interesting again because of this. It's not clear what effect it will have in places like VA-10, IL-06, GA-06, and TX-07 where, statistically speaking, everyone already had health insurance before Obamacare.