Democratic presidential nominee Hillary Clinton’s staff said it would be “lethal” for the former secretary of state to support taxing carbon dioxide to fight global warming, according to hacked emails.

Campaign spokesman Brian Fallon sent an email to campaign manager Robby Mook inquiring about a Politico article quoting New York Democratic Sen. Chuck Schumer saying a carbon tax would be politically possible if Clinton wins in 2016.

“Policy, is there any chance we go near such a proposal or can we nip this in the bud tonight?” Fallon asked in a June 2015 email released by WikiLeaks.

“I don’t recall any polling to guide us, but I’d be a bit nervous about rushing to say we’d never support such a tax,” Mook responded. “Bernie I assume DOES support such a tax and it could be fodder for him if we say unequivocally now that we don’t support one.”

The email was one of thousands released by WikiLeaks from Clinton ally John Podesta’s hacked Gmail account. The emails give an inside look at how the Clinton campaign carefully plotted out talking points on key issues, like energy and global warming.

Staffers, for example, spent months carefully concealing Clinton’s position on the Keystone XL oil pipeline — even cutting a section on the project out of her book “Hard Choices.”

The Clinton campaign also had doubts about echoing primary opponent Vermont Sen. Bernie Sanders’ support for a carbon tax.

“To be clear: it’s lethal in the general, so I don’t want to support one,” Mook wrote to Fallon. “But don’t want to give bernie contrast right now. So if there’s a way to re-state principles and say she’ll announce something in the next few weeks, that would be great.”

Carbon taxes were all the rage among Democratic lawmakers in 2015, and Politico quoted Schumer saying if “Hillary wins and we take back the Senate, I believe many of our Republican friends will say we’ve been starving the government for revenues.”

“I think in 2017 people of both parties might come to that as the best way to fund the government,” Schumer said, implying Republicans would go along with a tax because of political pressure.

The Democratic Party 2016 platform endorses a carbon tax. The platform says “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.”

Clinton, however, has not come out in favor of such a tax, though her campaign said she would be open to Congress proposing its own carbon tax.

“Right now we’ve not proposed a carbon tax,” Podesta told reporters at the Democratic National Convention in Philadelphia. “We believe we can get the job done. But if Congress wants to come forward with one, we’ll take a look at it.”

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