U.S. Democratic Rep. Gary Peters talks to reporters before turning in signatures to run for Michigan's U.S. Senate on Monday, April 21, 2014 in Lansing, Mich. The third-term congressman from suburban Detroit, hoping to succeed retiring Sen. Carl Levin, submitted 26,000 signatures a day before Tuesdayâs deadline. (AP Photo/David Eggert)

DETROIT -- Conservative operatives backed by the Koch brothers aren't very big fans of Rep. Gary Peters. But that's OK, because he's not a big fan of them either.

Peters, a three-term Michigan Democrat now making a bid for the Senate, has drawn fire from Koch-backed groups like Americans for Prosperity (AFP) over health care reform and carbon regulations. AFP has already spent more than $5 million this election season on television ads targeting Peters.

The latest poll shows Peters up 9 points against Terri Lynn Land, Michigan's former secretary of state and Peters' likely opponent in the general election. (The Michigan primary won't be held until August 5.) But Peters is expected to face a tough Senate race in November, and the ad wars are already well underway.

"I feel like l'm not really running against Terri Lynn Land. I feel like I'm running against the Koch brothers," Peters said at a campaign rally in Detroit on Friday. "That's who I'm really running against here."

But rather than dodging the attacks, Peters is meeting them head-on.

Friday's rally featured an appearance from Democrat Debbie Stabenow, who will be Michigan's senior senator now that fellow Democrat Carl Levin is retiring. It also brought in some progressive star power with Sen. Elizabeth Warren (D-Mass.). Both Warren and Peters had appeared that morning at Netroots Nation, an annual meeting of liberal bloggers and organizers held in Detroit's Cobo Center.

At the rally, Peters joked that his wife, Colleen, has seen him on television more than in person during the campaign. "That's a problem, because all the ads you see, they're all negative ads," said Peters. "When you see my wife, tell her I'm a nice guy, please."

The AFP ads aimed at Peters have focused mainly on his support for the Affordable Care Act. Peters, for his part, has been on the attack against the Kochs themselves on another issue: petroleum coke. Last year, Koch Carbon, a subsidiary of Koch Industries, drew national attention for letting massive piles of petcoke, a byproduct of petroleum refining, sit in Detroit. The piles were creating huge clouds of dust over the city.

Peters spoke out against the petcoke piles and against Koch Carbon, and introduced legislation calling for a federal study on the health and environmental impacts of the product. The piles were moved earlier this year, but there's an ongoing political and regulatory battle about where they should ultimately go.

Peters spoke about the petcoke issue Friday. "I am not going to let the Koch brothers pretend as if they care about the health care of Michiganders," said Peters. "We remember those piles that were piled up just down the river from where we are now ... They care about their agenda, which is weakening environmental laws. It's about being anti-middle class, about tax breaks for millionaires. We are going to tell them in no uncertain terms this election that Michigan is not for sale. The people of Michigan get to determine who is going to be their next senator."

Peters has emphasized environmental issues during his campaign, calling for reduced greenhouse gas emissions -- another area where AFP has gone after him. But Peters told The Huffington Post on Friday that he doesn't think the AFP attacks will be a problem for him. "I think people understand it's important, and they expect people who are running for elected office to stand up and take a stand and show some courage," he said.