Democrat Debbie Mucarsel-Powell unseated Republican Rep. Carlos Curbelo to represent Florida’s 26th District in Congress by 1 percentage point on Tuesday.

The race was close and it prompted Republicans to pursue an unusual line of attack during the campaign: The National Republican Congressional Committee launched an ad painting Mucarsel-Powell as beholden to fossil fuel interests.

First, please watch the ad. It is breathtaking:

Among the allegations the ad makes is that Mucarsel-Powell takes money from “shady characters.”

“… we learned that her family profits off a company that repeatedly violates environmental laws and her campaign is flooded with dirty coal money, the very polluters that threaten our way of life in the Keys,” says the narrator, while text reading “The Florida Keys … at risk … as a result of climate change” flashes on the screen.

Is this accurate? According to the Federal Election Commission, Mucarsel-Powell raised more than $3.7 million for her campaign to date. The largest single donation, $262,057.60, came from the House Victory Project, which funds Democratic congressional campaigns.

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The Center for Responsive Politics compiled a list of her top donors. The contributions seem to come mainly from PACs, venture capitalists, and private equity firms. The venture capitalists and private equity firms could have coal assets in their portfolios, but it’s hard to say for certain. The NRCC did not respond to requests from Vox for clarification on what they were referring to with this allegation at the time of writing.

According to a Florida Democratic Party spokesperson, the “coal money” the ad refers to is a $2,700 donation from Tom Steyer, a billionaire donor to progressive causes, including climate change legislation. A document produced by the NRCC notes that his hedge fund, Farallon Capital Management, invested millions in coal-fired power plants under his watch. Steyer has since left the fund is now actively campaigning against fossil fuels.

Now let’s look at who is paying for this ad: The NRCC is the main fundraising arm for congressional Republicans, with more than $174 million raised in the current election cycle. Here are some of their largest donors this election cycle, according to the Center for Responsive Politics:

You’ll see that one of the largest single donations comes from Chase Koch, son of billionaire Charles Koch (his name appearing on the list twice may be an error). And Chase’s company Koch Agronomic Services is a subsidiary of Koch Industries, a conglomerate with many oil and gas interests that is partially owned by Charles Koch. The elder Koch and his brother David are major funders of dark money groups that oppose climate change policies, helping push President Trump to withdraw the United States from the Paris climate agreement.

Further down the list is Kelcy Warren, the billionaire CEO of Energy Transfer Partners, the company behind the Dakota Access Pipeline, a proposed oil pipeline in North Dakota that sparked massive protests from indigenous groups and environmentalists.

So why would a group funded by fossil fuel interests opposed to fighting climate change run an attack ad criticizing a candidate for taking coal money and being weak on climate change?

Because this could be the one race where such an argument might make sense.

Florida might become the United States’ climate policy bellwether

While the Republican Party as a whole may be apathetic at best and denialist at worst about climate change, in Florida, with 1,350 miles of coastline, the environmental crises are impossible to ignore.

The sudden ramp-up and vast destruction from Hurricane Michael last month was fresh in the minds of many Floridians when they went to the polls. Storms like these are exacerbated by warmer water and rising sea levels from climate change. Florida cities like Miami are also seeing year-round flooding at high tide as sea levels rise.

But just a few years ago, Florida officials were banned from using the terms “climate change” and “global warming.” So it remains a contentious issue.

The race in the 26th District was particularly interesting: This district is at the state’s southern tip and includes the Florida Keys, an archipelago threatened by extreme weather and rising seas. It was also hit very hard by Hurricane Irma last year.

The incumbent Republican, Carlos Curbelo, made fighting climate change a part of his platform; he was a member of the bipartisan Climate Solutions Caucus and introduced a bill to impose a price on carbon in July. This sets him apart from many of his Republican colleagues.

It’s hard to say whether the attack ad swayed any voters, but Curbelo couldn’t thwart the challenge to his seat.

Mucarsel-Powell also made climate change a key element of her platform. “Through my work at the Coral Restoration Foundation, I’ve worked to slow the impact of climate change on our marine life and our reefs,” she wrote on her website. “I’m committed to investing in clean energy and innovative infrastructure, not just to move us to a low fossil fuel economy but also to protect our communities from sea-level rise.”