"I just think the Democrats don't need anymore bad news and this is just a headache that they don't need to deal with," said Nathan Gonzales, political editor at the non-partisan Rothenberg Political Report.
Quinn faces a tough re-election himself for the seat he occupied after Gov. Rod Blagojevich was ousted.
"I think voters have really begun to focus in on the Democratic side and ask themselves, is it really enough not just to be Rod Blagojevich," Chicago Tribune's veteran political reporter Rick Pearson said on "Top Line" last week.
The state controversy trickled into the national limelight, and threatened to worsen the perception of Illinois politics or "Chicago-style" politics that Republicans have seized on. But despite its Hollywood script and scandal, observers said the Cohen saga is unlikely to hurt Democrats in the long term.
"I don't think that it's going to have an electoral impact outside of Illinois in November," Gonzales said. "I think that this election is going to be about broader themes on economy [and] direction of the country."