House Majority PAC, the major Democratic super-PAC working to elect Democrats to the House, is going on air with another ad supporting Rep. Nick RahallNick RahallLikely W.Va. Senate GOP rivals spar in radio appearances West Virginia is no longer Clinton country Solution needed: Rail congestion is stifling economic growth MORE (D-W.Va.).

The ad goes on offense against Rahall’s Republican opponent, state Sen. Evan Jenkins, charging he tried to delay a water safety bill meant to prevent a chemical spill similar to the one that recently devastated parts of the state.

The spot goes on to tie Jenkins to the billionaire Koch brothers, Charles and David, who have poured millions into competitive House and Senate races — including hundreds of thousands into Rahall’s district — hammering vulnerable Democrats.

It says that Freedom Industries, which caused the spill, is a “corporate partner” of the Koch brothers and suggests after Jenkins opposed the water safety bill, his Koch support increased.

“Dirty money for Evan Jenkins is polluting West Virginia,” a narrator says.

The ad is backed by at $65,000, weeklong buy.

Rahall is one of Democrats’ most vulnerable incumbents and has already faced heavy attacks from GOP groups, including the hundreds of thousands from Koch-backed groups.

A report out this weekend from CNN revealed the attacks appear to be getting to the congressman, as he contemplated retiring, but House Democratic leadership promised him more campaign funds to stay in the race.

Andy Sere, Jenkins's campaign adviser, pointed to that report and suggested House Majority PAC's spending in the district might be a "waste."

“Far be it from me to tell House Majority PAC’s anti-coal donors how to spend their money, but isn’t it a waste trying to bail out a guy who’s down 14 points and knows he’s in such bad shape that he considered dropping out the race a couple weeks ago?" he said.

— This piece was updated at 11:45 a.m. to correct Andy Sere's position with Jenkins's campaign.