Their intimidation tactics may have backfired on them as far as polling goes; usually the democong "find" just enough votes in the trunk of some poll worker's car to put them over the edge.
Having the right amount of ballots ready requires some level of accurate polling, but with the D+10, or +15 samples they were taking to skew the media propaganda, they weren't going to get accuracy.
On top of that, I think people weren't being honest with the polls (who wants the pollster to know you are deplorable)
Finally, there are probably more than a few things which threw the political class off the tracks; we were talking a coupla days ago about Rust Belt voters