Democrats think their get-out-the-vote technology will ease the coming pain on election day.
On election day itself, the DNC can spend time and money on the "knock and drag" -- it will have a pretty good idea, down to the individual voter, of who it needs to turn out in order to be competitive in House districts. Republicans have access to the same technology, but there are doubts within the party about whether the RNC has the metabolism and structures to build votes like the Democrats. Republicans in places like Ohio are just this cycle beginning to focus hard on the early vote. Democrats have been doing this for several cycles.
If the reports of voter enthusiasm are accurate, dragging voters to the poll may be the Democrats' only hope. Drag and keep them there while the hoards of Republicans cast their vote - willingly.