In some districts, maybe they can. In other districts they can’t win if ANY groups of voters who supported them in the past stay home.
Keep in mind mainstream dems are not the ones out there who've gone all maniac. A lot of them are fed up enough to avoid the mid-terms.
Beyond all of that, it would be wonderful if Republicans in DC did what's right. That would be to pass a health care solution that restores our freedom and doesn't reward deep-pocket donors.