In a rare moment this election season, Republican Sen. Kelly Ayotte and Democratic Gov. Maggie Hassan agreed on something.

Of course, it wasn’t Social Security or gun rights, something the two nominees for the New Hampshire Senate seat constantly go back and forth on, but nonetheless, it could become an important policy issue that Congress considers in the coming years.

Both Ayotte and Hassan are against instituting a carbon tax — at least for now.

The idea of a carbon tax — a form of carbon pricing on fossil fuels, especially those used by motor vehicles, that is intended to reduce carbon dioxide emissions into the atmosphere — is not a new one.

It’s been around for years, but as a result of the Paris Climate Agreement last year and President Barack Obama’s Clean Power Plan, it’s an idea that’s seriously being discussed again. A similar national cap-and-trade plan was hotly debated in 2009 when Democrats had taken full control of the White House and Congress, but it failed to pass.

When asked if Ayotte supported a carbon tax, Liz Johnson, the Republican incumbent’s spokeswoman, bluntly said, “she does not support a carbon tax.”

Hassan, on the other hand, said in a Concord Monitor editorial meeting this month that she wouldn’t support initiating a carbon tax “right now.”

People could read a lot into her vague answer. Her rhetoric matches the language used at the top of her ticket.

Democratic presidential nominee Hillary Clinton has not come out directly supporting a carbon tax, but she has left the door open to support it at a later time. Her primary rival, Sen. Bernie Sanders, D-Vt., is a proponent of the tax and pushed to make it part of the Democratic platform.

“Democrats believe that carbon dioxide, methane, and other greenhouse gases should be priced to reflect their negative externalities, and to accelerate the transition to a clean economy and help meet our climate goals,” the platform states.

Although a carbon tax isn’t specifically mentioned, it is one of the possibilities, including cap and trade, that could be introduced to limit carbon emissions.

But Clinton still struggles with her position on the issue. The latest WikiLeaks email dump shows how her campaign thought a carbon tax was political poison.

In January 2015, campaign director John Podesta sent an email to aides saying, “We have done extensive polling on a carbon tax. It all sucks.”

Podesta later said at the Democratic National Convention in July that, “if Congress wants to come forward with [a carbon tax proposal], we’ll take a look at it.”

Hassan could be following Clinton’s lead on the issue, which doesn’t necessarily help her shake the image of being a “Democratic rubber stamp,” something Ayotte’s campaign is trying to paint her as.

But Hassan’s hesitance on implementing a carbon tax could also reflect the sentiments of her state. The residents of New Hampshire enjoy not having to pay a lot of taxes. In the interview with the Concord Monitor, Hassan also said she was opposed to increasing the federal gas tax.

In an election year, it’s not surprising that Hassan would want to play it safe and say she would not want a carbon tax yet in such an anti-tax state.

Robert Mohr, professor of economics at the University of New Hampshire, said it could be difficult for lawmakers to express their opinion on a carbon tax to their constituents.

“It is tough to fit into a sound bite and a political commercial talking about the tax,” Mohr, who specializes in environmental economics, said. “I think members of both parties struggle when talking with constituents about some of the specifics of the regulations.”

Hassan isn’t the only Democrat who doesn’t fully support a carbon tax. In an attempt to get lawmakers on the record about their opposition to a carbon tax, Republicans introduced a non-binding resolution that was voted on in the House in June. Six Democrats joined Republicans saying they don’t support it.

Democratic Reps. Brad Ashford (Neb.), Sanford Bishop (Ga.), Henry Cuellar (Texas), Ann Kirkpatrick (Arizz.), Collin Peterson (Minn.) and Kyrsten Sinema (Ariz.) said they did not support a carbon tax.

The vote against a carbon tax for Peterson, Cuellar and Bishop stands in stark contrast to their votes in favor of 2009 legislation to essentially impose a carbon price.

In 2013, the Senate also took a symbolic vote on carbon taxes, which brought eight Democrats to oppose them, including Sens. Max Baucus (Mont.), Mike Crapo (Ind.), Heidi Heitkamp (N.D.), Mary Landrieu (La.), Joe Manchin (W.Va.), Claire McCaskill (Mo.), Mark Pryor (Ark.) and Jay Rockefeller (W.Va.).

It’s interesting to look at the states where these representatives come from and why they voted that way.

“Geographically, there are going to be differences on how different regions are affected [by a carbon tax] and how they [lawmakers] tackle a carbon tax,” Mohr said.

And he’s right. The Democratic lawmakers from the states with significant coal production tend to vote with Republicans on opposing a carbon tax.

Arizona, Arkansas, Indiana, Louisiana, Missouri, Montana, North Dakota, Texas and West Virginia are consistently in the top 25 states of coal production, according to the U.S. Energy Information Administration.

A carbon tax could hurt the coal industry as it encourages investment in renewable energy resources, so it makes sense that legislators from coal-heavy states might oppose a carbon tax, even if they are Democrats.

That’s especially true if they receive campaign contributions from these industries. A quick look at the House members who voted on the resolution this year shows two of the members receiving money from groups who oppose a carbon tax.

At the time of the vote, Bishop received $5,000 and Cuellar received $28,500, according to MapLight, a nonpartisan research organization tracking money’s influence in politics.

Environmental groups have not been playing a significant role in the New Hampshire Senate race, though. The Sierra Club, the nation’s largest environmental advocacy group, endorsed Hassan this year and has only put forward $140 to support the Democratic nominee, according to the Center for Responsive Politics, which also tracks money in politics.

Ayotte has earned the endorsement of the conservative clean energy group ClearPath Action Fund, and the Environmental Defense Fund last year ran a five-figure online campaign for her support of the Clean Power Plan. The network funded by the libertarian billionaire Koch brothers specifically cites Ayotte’s support for environmental issues as a reason it is not aiding her reelection campaign.