This is my take away too. The top of the ticket underperformed relative to the rest. In Pennsylvania Harris lost by 2 point, but Casey only seems to be down half a point for retaining his senate seat and that is headed for recount. The Pa state house held its single seat democratic majority.
The only explanation that seems reasonable to me is that the election hinged on the large center of mostly low information voters deciding that Trump bringing the circus back to Washington was less bad than their grocery bill(I am NOT saying they are correct to blame the current administration, just that they are).
tl;dr [that Carville quote]
I guess this is what happens when you fail to teach an entire generation to read.