If it's Hillary vs. Donald...

[Fuzzybigfoot]

Would Hillary's coattails be big enough for the Democrats to take back the house?

[JonathanSwift]

No.

[Brittain33]

Yes. But he can't possibly become the nominee.

[Cory]

Probably not. The coattail effect has always been overestimated.

[dudeabides]

No because every Republican running would distance themselves from Trump.

[Brittain33]

It's not Hillary's coat tails that would do it.

It would be millions of Republican-leaning voters staying home because Trump. It's easy to forget that a large number of voters don't really care about their downballot votes and will just support their party's candidates, and if they don't come out, you are screwed.

[Amenhotep Bakari-Sellers]

I wouldn't rule it out. But, senate is more likely to flip; if the Dems get on a roll there, it is possible. But Dems would exceed expectations.

[Vosem]

McGovern and Mondale failed to appreciably hurt the bottom of the ticket, and I don't think Trump would either. The candidates would individually distance themselves from him. A mid-single digits Clinton victory (like Obama/Romney, or maybe a bit stronger) would be best; anything stronger than that, and down-ticket races start divorcing themselves from the presidential ones.

The exceptions are elections where power shifts on the presidential level (1952, 1980, 2008). But landslides for incumbents don't normally translate to large downballot gains; 1964 is the only time that's happened post-WW2.