Calhoun,
They may be terrified of losing the senate, but they aren't desperate. They'd have done this anyway. There's no-one to hold the DOJ accountable so what's the downside? Hopefully Rounds has enough money left in his campaign to run enough ads to counter this. I'd think he'd need to be highly aggressive about it though.

Stupidity is expensive
If you find yourself in a fair fight, your tactics suck!