“What tools do the Democrats have at their disposal to turn this growing tide back around?”
Massive election fraud as is standard operating procedure.
The entire notion that Hillary could not possibly be defeated just reeks of confidence that they were going to stuff the heck out of the ballot box. I think part of the Democrat shock in 2016 is that they KNOW they stuffed the ballot box -- and it wasn't enough. Of course they should try to outdo themselves in the mid-terms, but as their efforts become more and more Herculean, it may get easier to reveal their tricks. Trump has his hands full with a lot of important issues but I hope he surprises us with some sunlight about how Democrats have won in the past.
That, combined with the current FBI/DOJ scandal could really make a difference at the polls in November. Fraudsters may be afraid to commit their fraud and patriots may be energized to go out and drain the swamp.