Few House races better capture the way outside interest groups have taken over campaigns than the Member-vs.-Member face-off between Republican Jim Renacci and Democrat Betty Sutton in Ohio’s 16th district.

It’s not just the incessant TV ads that have saturated the airwaves so thoroughly that, as one Renacci aide put it, voters “can’t even tell which candidate’s which at this point.” It’s also the bundles of glossy campaign literature stuffing voters’ mailboxes, the radio spots, Web ads, the canvassers who call day and night.

Both Sutton and Renacci say the barrage of outside spending has left voters bewildered and overwhelmed and has made it tougher for the candidates themselves to cut through the clutter. From big-spending labor unions and business-friendly trade groups to gun advocates, abortion opponents and animal rights groups, every issue group on the map seems to have a stake in the race.

Outside spending is soaring nationally in the first presidential race since the Supreme Court’s 2010 ruling that deregulated political spending. Spending by nonparty outside groups totaled $608.6 million as of mid-October, according to the Center for Responsive Politics. That’s more than twice the $301.7 million such organizations spent on the 2008 elections. 

In the redrawn 16th district, outside spending has hit $5.4 million, by the center’s tally, double the $2.7 million the candidates have doled out from their campaign accounts. Activists have flocked to the race because of the sharp contrast between the business-friendly Renacci and Sutton, a three-term House Member and daughter of a boilermaker.

“It’s massive noise, and it makes it more difficult for voters to size up candidates,” said Sutton, who has co-sponsored bills to improve campaign disclosure, match small donations with public funding, and amend the Constitution to reverse the 2010 Citizens United v. Federal Election Commission ruling.

Renacci, who’s seeking a second term, is no happier with the system, but he opposes sweeping new restrictions. Outside groups bombarded him with negative ads in 2010, he recalled, to little effect.

“I’m a big believer in the First Amendment,” Renacci said. “So I’m not going to gripe about the outside spending. Because political speech in America is one of the most protected forms of speech. And I think if we start talking about [restricting] those dollars, we’re going down a pretty slippery slope.”

Voters in the Northeast Ohio district, which is also ground zero for the presidential race and a hotly contested U.S. Senate contest, are all but disgusted, said Jim Meffert, executive director of Jefferson Action, a nonpartisan group focused on civic engagement. Participants at a Jefferson Action focus group were agog when they learned how badly the candidates were being outspent by interest groups, Meffert said.

“They were angry,” he recalled. “It was really extremely frustrating for them to see how much money was being spent by people who had no connection to the district, to attack somebody they didn’t like or didn’t agree with.”

Outside groups counter that they have a right to be heard. The Citizens United ruling has allowed the National Federation of Independent Business to engage in more races than before, said Lisa Goeas, vice president for political and grass-roots operations. 

The NFIB has spent a little more than  $90,000 on issue and digital ads for Renacci, who has a 100 percent voting record with the group, Goeas said. The new rules “level the playing field,” and if the NFIB didn’t weigh in, its opponents would, she added.

“We just feel like our voice needs to be heard, and we need to be part of the process,” Goeas said.

One of Renacci’s biggest backers has been the Congressional Leadership Fund, a GOP-friendly super PAC that plans to spend at least $2.6 million on his behalf. One of the super PAC’s ads portrays Sutton as a puppet-style bobble head voting with House Minority Leader Nancy Pelosi (D-Calif.) “99 percent of the time.” 

The National Republican Congressional Committee has spent $1.3 million to the Democratic Congressional Campaign Committee’s $290,000. The DCCC plans to spend up to $1 million, a spokeswoman said, but labor spending may have eased the pressure. 

The American Federation of State, County and Municipal Employees and the Service Employees International Union have spent close to $2 million on Sutton’s behalf. One AFSCME ad features a stewardess in a red kerchief, announcing pleasantly: “On behalf of Congressman Jim Renacci, thank you for flying Outsourcing Air, now sending Ohio jobs to China and India.”

A new player in 2012 is the Democrat-friendly super PAC called the House Majority PAC, which has gotten a fundraising assist from Pelosi. The super PAC has spent close to a half-million dollars on Sutton’s behalf and has coordinated messaging and ad timing with labor and environmental groups.

One of those is the Sierra Club, which has spent some $55,000 on Sutton’s behalf and loaned her two full-time staff members for organizing and field work. 

“We really believe that in a broadly political environment, where there’s more money than ever being spent … the way you’re going to win these campaigns at the margins is through these one-on-one conversations,” said Cathy Duvall, the Sierra Club’s national political director.

Smaller-spending groups include the National Rifle Association and the Humane Society Legislative Fund, which distributed a flier with a kitten and  puppy announcing they would “vote” for Sutton. Also engaged: Friends of Democracy, a pro-campaign-reform super PAC that plans to spend about $200,000 on direct mail backing Sutton. 

Super PACs have had less impact in the presidential contest but could prove effective in House races, said Friends of Democracy co-director David Donnelly: “These [PACs] are really going to have a dramatic impact downballot, particularly in House races that are beginning to tighten up.”

Correction: Oct. 18, 12:13 p.m.

An earlier version of this article misstated the group that distributed a flier on behalf of Rep. Betty Sutton (D-Ohio). The group was the Humane Society Legislative Fund.