People forget how unpopular both of these candidates are. Trump is such a bad candidate that split-ticket voting will be at record levels by default, like in 1996. Most incumbents simply don't lose by wide margins, unless they're Blanche Lincoln.
In 2008, there was a backlash against pretty much all Republicans and the entire GOP. That is not the case this year.
The electorate was far less polarized in 1996.
True, but there are plenty of NeverTrump Republicans who will continue to vote for downballot Republicans.