Republican senators are using opposition research to attack GOP challengers earlier and more aggressively than in past elections.
These senators are eager to avoid the fate of colleagues who lost to tea party-backed rivals they had shrugged off.
In Kentucky, the tea party-backed challenger to Sen. Mitch McConnell is trying to explain old investor letters that recently surfaced. The letters bear his signature and undermine his criticisms of a government bank bailout.
In Kansas, the physician trying to oust three-term Sen. Pat Roberts is apologizing for posting graphic images of gunshot victims on his Facebook page some years ago.
Both stories have the markings of "opposition research." That's the term for time-consuming digging into documents that campaigns often do.
Traditionally, Republicans and Democrats have aimed such efforts at each other.