Shortly after the 2012 election, John Podesta was invited to speak at a board meeting of the American Petroleum Institute. Podesta is an outspoken environmentalist who served as Bill Clinton’s White House chief of staff and then founded the Center for American Progress, an influential liberal think tank. A.P.I. represents the interests of the oil-and-gas industry.

At the meeting, Podesta was paired with Ed Gillespie, a former chairman of the Republican National Committee, and the two men discussed the November election results. “He was despondent and I was very cheery,” Podesta told me in August. Taking advantage of the unique opportunity to address his political opponents, Podesta told the oilmen that Republicans had made a “horrible error” in how they handled the controversial Keystone XL pipeline, which would carry oil from Alberta, Canada, to refineries in the Gulf of Mexico.

Keystone opponents, like Podesta, insist that the project would significantly increase carbon emissions by rapidly accelerating the development of the oil sands. Supporters of the project argue that with or without the pipeline, the Alberta oil sands will still be exploited, and therefore there would be no difference in emissions. With the help of heavy lobbying from A.P.I., Republicans in Congress tried to force the Obama Administration to approve the project. But in 2012, the State Department, which is in charge of the permit process for the pipeline—because it crosses an international border—opted to delay its decision instead.

Podesta argued that Keystone XL had been “rolling toward approval” before the G.O.P. put pressure on Obama. Their forceful efforts to get it approved, he argued, had backfired spectacularly on A.P.I. “The Republicans did the President a humongous favor by forcing a decision that he could only say no to, which was in fact their intention,” he told me, recapping his remarks at A.P.I. “They wanted to force him to say no, so they could campaign against him. And they spent a ton of fucking money in 2012 running advertising against [Democratic] members and against the President on this question, to no effect. All they did was put off the decision long enough so that you could mount a serious campaign against it.”

As I reported in September, in an article about the billionaire anti-Keystone activist Tom Steyer, Podesta helped organize that campaign.

“I told them that changed the odds from a virtual certainty—ninety-five to five—that he’d approve it, to probably fifty-one to forty-nine that he would not approve it,” Podesta said. “And so the blood drained from their heads! I probably said that for effect. I probably didn’t quite believe what I was saying. It probably actually had been reduced to sixty-forty that he’d approve it. But I think now it’s a fifty-fifty proposition.”

Earlier this year, the State Department, in a draft environmental-impact statement, said the pipeline wouldn’t have much impact on climate change. But the Environmental Protection Agency challenged that assessment, and State is now completing a final study of the competing claims that is expected to be released in the coming weeks or months. (The State Department refuses to give an exact date.) Once the report is finished, the ultimate decision about whether to build the pipeline will rest with Obama. In a speech in June, Obama said he will approve Keystone only if it “does not significantly exacerbate the problem of carbon pollution.”

On Tuesday morning, the Obama Administration announced that the President will have a new White House adviser to help him navigate these tricky issues about energy and climate: John Podesta. While Obama has privately expressed skepticism toward environmentalists’ claims about the pipeline, one of his closest counselors will now be a committed advocate for cancelling it. Naturally, proponents of the Keystone XL pipeline are nervous about Podesta’s new job, while Podesta’s allies in the anti-Keystone movement are ecstatic.

Podesta told me earlier this year that his case against Keystone was twofold. One, he believed the weight of the evidence suggested that the pipeline would indeed accelerate the production of oil from the oil sands and increase greenhouse-gas emissions over the long term. “There’s a lot of oil flowing from there, right? They’re not gonna stop doing that. But do we want to facilitate supercharging that?” he said. “That’s the question. And the answer to that I think is no, because of the climate impact.”

He was emphatic that Obama’s own test cannot be met. “I think he should not approve it,” Podesta said. “I’m of the view that you just can’t meet the standard now that Obama set out: Does it or does it not significantly exacerbate the problem of carbon pollution? What are the net effects? And I think a fair review of that would say the net effects are big and they’re negative.”

In his interview with me, Podesta also argued that if Obama wanted to get anything accomplished in a second term, the President had to be expansive in his use of executive power. Climate-change policy, Podesta believes, is fertile ground. Without any involvement from Congress, Obama’s E.P.A. can implement regulations to dramatically reduce carbon emissions, and the President could set a new course on energy policy by cancelling Keystone.

“We don’t know at the end of the day how you change the national and global mindset,” Podesta told me. “But if Obama did say no, what does that do to finally force some tough decision-making into the climate world? It could have a fairly significant impact on people’s understanding about what the problem is and the cost of adapting to a warming planet.” For Podesta, a decision by Obama to cancel the Keystone XL pipeline could be a turning point in the larger fight against global warming—a moment, he said, that could begin “to reverse” the effects of climate change.

Update: A White House aide e-mailed late on Tuesday to say that Podesta would recuse himself from working on the Keystone Pipeline decision.

“In discussions with Denis,” the aide said, speaking of the White House Chief of Staff Denis McDonough, “John suggested that he not work on the Keystone Pipeline issue, in review at the State Department, given that the review is far along in the process and John’s views on this are well known. Denis agreed that was the best course of action.” Podesta’s climate-change portfolio will therefore be limited largely to overseeing the implementation of E.P.A. regulations, which are already moving along, and not the far more controversial and politically sensitive decision about the pipeline.

Still, Podesta is on the record as strongly opposing the pipeline. If Obama approves the project, he will have to do so knowing that he is contradicting the assessment of his new climate-change adviser.

Photograph by Chip Somodevilla/Getty.