A Republican senator facing a tough reelection fight is supporting President Obama’s signature climate change rule.

Sen. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (N.H.) came out in support late Sunday of the Environmental Protection Agency’s (EPA) regulation that seeks a 32 percent cut in the power sector’s carbon dioxide emissions.

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Ayotte, who faces a tough reelection bid in a state that voted for President Obama in the last two presidential cycles, is the first congressional Republican to openly endorse the rule, dubbed the Clean Power Plan.

“After carefully reviewing this plan and talking with members of our business community, environmental groups, and other stakeholders, I have decided to support the Clean Power Plan to address climate change through clean energy solutions that will protect our environment,” Ayotte said in a statement.

“New Hampshire is already well on its way to meet the goals of the Clean Power Plan through positive steps it has already taken,” she continued, saying she would closely monitor the regulation’s implementation to ensure that the state has sufficient flexibility in complying.

New Hampshire Gov. Maggie Hassan Margaret (Maggie) HassanDemocrats step up hardball tactics as Supreme Court fight heats up Congress needs to prioritize government digital service delivery Senate Democrats demand answers on migrant child trafficking during pandemic MORE is seeking the Democratic nomination to face Ayotte and would be seen as a top-notch challenger. She's already attacked Ayotte on climate, signaling she intends to make it an issue in the race.

Hassan on Friday called for the state’s congressional delegation to support the climate plan. She accused Ayotte of siding “with corporate special interests over New Hampshire’s environment," arguing the senator had fought to protect tax breaks for oil companies and voted to block the EPA from moving forward with regulations to reduce carbon emissions.

Though only elected to the Senate in 2010, Ayotte has already shown a track record of bucking the GOP on climate.

She was only one of five senators to have voted in January to pass a non-binding amendment stating that “climate change is real and human activity significantly contributes to climate change.”

In July, Ayotte was the first recipient of a donation from Jay Faison, a Republican who has pledged to donate money in the 2016 election to encourage the GOP to recognize climate change and endorse conservative solutions to it.

Faison donated $500,000 to a super-PAC benefitting Ayotte.

NextGen Climate, the super-PAC run by billionaire environmental activist Tom Steyer, welcomed Ayotte’s position but pushed her to do more.

“Sen. Kelly Ayotte today recognized a simple political fact: New Hampshire voters overwhelmingly support policies like the Clean Power Plan that save lives, lower energy costs and address climate change,” Mike Padmore, the New Hampshire director for the group, said in a statement.

“Now it’s time for Sen. Ayotte to show that she truly supports America’s clean energy future and commit to achieving more than 50 percent clean energy by 2030,” he said, repeating a challenge Steyer has made to all political candidates in the 2016 cycle.