Something that folks aren't mentioning...
The fact that Democrats are neck and neck with Republicans in many of these races is a phenomenon in itself, as the current President's party ALWAYS loses in the midterms badly.
The fact that Dems are making these races competitive shows that something is up and something is changing. They could lose every single race and I would still count it as a success due to the fact that they have been out here hustling and making Republicans work for it.
As it stands, they won't lose every single race though.