Former North Dakota Attorney General Heidi Heitkamp (D) is running for the U.S. Senate by touting her independence, as seen in her latest ad, which highlights, among other things, her support for Republican-friendly energy policies.

"I will put North Dakota's priorities first, and that means standing up for our farmers and ranchers and standing against 'one size fits all' rules from Washington that would put thousands of jobs in our energy industry at risk," Heitkamp said in a statement announcing the ad.

Being seen as independent is probably crucial for a Democrat in a red state like North Dakota. But Heitkamp's stances could also put her at odds with some of her biggest backers, including donors. Take the battle over hydrofracturing, or fracking, to extract natural gas from deep underground.

According to campaign records tallied by the Center for Responsive Politics, Heitkamp's second-largest group of contributors are employees of Weitz & Luxenberg, a mass tort law firm that has represented those arguing the harms of fracking in the past. The law firm's employees have given Heitkamp at least $22,400.

Environmental advocates are worried about the effects of fracking, including the potential to cause earthquakes and poison water supplies. Yet Heitkamp has decried those concerns as stemming from "junk science."

As an electoral strategy, it seems to be working. Although North Dakota leans Republican, many observers rate the Senate race a tossup.

A spokesman for Heitkamp did not immediately answer a request for comment.

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