The latest automated poll conducted by SurveyUSA has Roberts up by 20 points — narrower than his 33-point edge a month ago. Although Roberts still holds a solid lead, in the aftermath of House Majority Leader Eric Cantor’s shocking primary defeat, even a 20-point gap isn’t enough to comfort establishment Republicans when the trend line is moving in Wolf’s favor.

“It’s definitely closer than we expected,” said one GOP operative close to the race on Roberts’ side.

Except for Wolf’s scandal, the conditions are favorable for an upset: Tea party groups who fell short in the Mississippi Senate race are turning their attention toward Kansas; Roberts, who has worked in Washington for 47 years (including time as a congressional staffer), is facing reelection in a cycle in which the anti-Washington sentiment is much stronger; and although Roberts took his challenger seriously, the establishment didn’t consider Wolf a major threat and didn’t come out on Roberts’ behalf as it did for Mississippi Sen. Thad Cochran.