What's the best *plausible* result for Democrats in 2018?

[King Lear]

My best plausible result for democrats is D+26 in the house and D+2 in the senate which would have them holding all their senate seats while flipping republican senate seats in Arizona and Nevada. This scenario would give them narrow majorities in both houses of Congress and would be a utter disaster for republicans, especially if trump still managed to win reelection in 2020 which would set them up for another midterm wipeout in 2022 followed by a landslide presidential defeat in 2024 and possibly decades in the electoral wilderness. The reason I don't believe democrats can have the massive house gains others are predicting is because their pathway back to the majority is heavily dependent on winning as many Clinton-Republican districts as possible (theirs 23 of them), holding on to all the Trump-Democratic districts (theirs 12 of them) plus winning a few marginal Trump-Republican districts. I just have a really hard time seeing democrats winning a bunch of districts trump won by double-digits with the exception of the few that are currently held by democrats.