When Rep. Kendra Horn (D-Okla.) heard Joe Biden say he would “transition from the oil industry” to combat climate change at the last presidential debate, she instantly felt troubled. “I definitely paused and had a reaction,” Horn recalled. “I disagreed with him.”

Biden’s words struck a very different chord with climate activist Evan Weber. “I was very happy to see the vice president be honest and go on offense,” said the co-founder of the youth-led Sunrise Movement.

For months, the Democratic presidential nominee has walked a careful line with policies and rhetoric calibrated to satisfy both sides of the long-simmering divisions in the Democratic Party over climate change, fossil fuels and how to talk about them in the campaign while seeking to head off attacks from Republicans. But in the last days of the race, that balancing act has been thrust into jeopardy, creating new challenges for Democrats up and down the ballot.

“Trump, he’s obviously looking for something to try and hang his hat on at this point, said Rep. Tim Ryan (D-Ohio), whose district abuts the border with Pennsylvania, a region where fracking is a major issue. “That’s what makes it difficult.”

The United States is already moving away from fossil fuels, and carbon emissions must go down by 7 percent each year by 2030 to avoid catastrophe, but President Trump and his allies seized on Biden’s comments throughout the weekend, portraying them as evidence that he is beholden to his party’s left wing and would eliminate many blue-collar jobs. Some moderate House Democrats in competitive districts where oil is an economic engine distanced themselves from the remarks. And liberals who championed a sweeping “Green New Deal” climate blueprint vowed to pressure Biden to go big on climate change if elected.

The effect has been a muddying of the Democratic Party’s stance, forcing Biden and other candidates into a defensive posture with just over a week until Election Day. Climate change has been one of the most politically vexing issues of the Trump presidency for a Democratic Party that is powered by an energetic liberal base but reliant on suburban moderates in the oil-rich Sun Belt and bent on regaining lost ground with White, working-class voters in the Rust Belt, whose jobs are often connected to fossil fuels.

While there is broad acceptance in the party that climate change is real and presents a dire threat, there is less consensus about how to meet the challenge. Equally unresolved is the question of how to pitch ideas to an electorate that includes working-class voters anxious about losing their jobs in a new energy economy and a younger generation that feels an urgency to reverse harmful trends in the environment.

Throughout his presidency, Trump has questioned the overwhelming body of climate research that says the planet’s warming is caused by humans, delayed and blocked climate reports from his own scientists and fought standards to lower vehicle emissions. He has campaigned aggressively as an uncompromising champion of fossil fuels and against Democratic environmental proposals.

His positions have alarmed Democrats, prompting many to set aside their own differences to support Biden. But climate and energy issues are expected to spark a fierce internal debate in 2021 if Democrats win the White House and the Senate, along with immigration and health care. A campaign season jolted by deadly wildfires and hurricanes fueled by global warming, on top of Biden’s sometimes controversial comments, has accelerated some of those conversations.

“Is my job to push the Democratic Party? Absolutely,” Rep. Alexandria Ocasio-Cortez (D-N.Y.) said in an interview Sunday on CNN’s “State of the Union.” A chief co-sponsor of the Green New Deal, Ocasio-Cortez offered subdued praise for Biden’s stance on fossil fuels as she talked up the importance of defeating Trump.

As for what comes after: “It would be a luxury for us” to be discussing “how we will push the next Democratic administration,” she said.

Biden has embraced an ambitious plan to end carbon pollution from power plants by 2035 and bring all emissions to net zero by 2050. At the same time, he has shown support for industrial unions and workers with a pledge not to end hydraulic fracturing, or “fracking,” despite the concerns of environmentalists. And he has rejected the far-reaching Green New Deal that liberal leaders have presented in response to the climate crisis.

Biden’s proposals were signals of how Democrats have focused on climate change with more urgency in recent years. President Barack Obama, for example, set more modest goals.

“Climate change is the existential threat to humanity. The existential threat to humanity. Unchecked, it is going to actually bake this planet. This is not hyperbole. It’s real,” Biden said on a Saturday episode of the podcast “Pod Save America.”

But Biden has at times been murkier in explaining how he’ll meet this challenge. The most recent example came in Thursday’s debate, when Trump asked Biden whether he would close down the oil industry.

Biden answered affirmatively. “I would transition from the oil industry, yes,” he said.

Biden and his aides quickly tried to clean things up, saying that he was talking about ending federal subsidies for oil companies and underscoring the long arc of his plan. “We’re not getting rid of fossil fuels for a long time,” he told reporters later that night.

By then, some moderate Democrats were already scrambling away from him. One of the most prominent was Horn, who flipped a Republican district in 2018 that includes Oklahoma City, one of the country’s oil capitals, and its suburbs. “Here’s one of the places Biden and I disagree. We must stand up for our oil and gas industry,” she tweeted.

“The reason that I wanted to articulate it is, I think, far too often, it’s too easy for people to oversimplify things and put people into categories that say you’re either with me or you’re against me,” Horn said in an telephone interview.

She said that she has heard some concerns from people in her district about Biden and that his plan is not feasible. She called for a “long-term, sustainable approach” that incudes oil and gas.

Among those who voiced concerns about Biden’s words was her Republican opponent, state Sen. Stephanie Bice. “90k jobs in Oklahoma — and @HornForCongress supports Biden,” Bice tweeted in response to a clip of Biden talking about oil in the debate.

Bice added in a statement Sunday that Horn’s “last minute pandering isn’t likely to work.”

Beyond Oklahoma, House Democrats in competitive races in New Mexico and Texas took issues with Biden’s remarks. Democrats have long hoped to turn Texas blue, and polls show Biden running competitively with Trump there. Republicans see Biden’s comments as a way to derail his momentum there.

“How about the other night of the debate? He was doing okay, he was doing okay. He was doing — and then the last question, I said, ‘You mean you’d get rid of oil?’ ” Trump said in North Carolina on Saturday. “He said, ‘Yes, I’d wean ourselves off of oil,’ ” Trump added mockingly.

Ryan, a Biden ally who represents a district with many White, working-class voters, said Biden should have emphasized that his transition would happen slowly, over decades. “We’re talking 10-year 20-year, 30-year plan here,” he said.

Campaigning in Pennsylvania on Saturday, Biden tried to set the record straight.

“Let me get something straight here, in coal country: I will not ban fracking — period,” Biden said at a drive-in rally in Luzerne County, Pa. “I’ll protect Pennsylvania jobs, period.”

Rather than highlighting his proposed transition away from oil, as he did in the debate, Biden talked up increased investments in carbon capture technology. “We’re going to get rid of the $40 billion in fossil fuel subsidies and we’re going to invest in clean energy and carbon capture,” he said.

One of Biden’s top aides also sought to assuage concerns about job losses in a television interview broadcast Sunday.

“He believes that we are not only going to create new jobs, we are going to maintain jobs. People are not going to lose jobs under a Biden administration,” Biden’s deputy campaign manager Kate Bedingfield said in an interview broadcast Sunday on NBC’s “Meet the Press.”

But in the Democratic Party’s liberal wing, no such reassurances were needed.

“He answered clearly that the United States does have to transition off oil and that Joe Biden has a plan to move America towards clean energy, that the climate crisis demands that and, in fact, it’s already been underway,” said Weber.

Indeed, the United States has already started to move — at a snail’s pace — in the direction Biden favors to offset the impacts of human caused climate change. The U.S. economy is still heavily dependent on refined oil that fuels millions of motor vehicles and natural gas that warms homes, but alternative energy sources are starting to offset the dominance of oil.

Even in Pennsylvania, where Biden is seeking not to be painted as an enemy of fossil fuels, 74,000 people have jobs linked to clean energy, more than the 23,000 who work petroleum-based jobs. Texas leads the nation in wind-power generation, forging so far ahead that clean-energy companies are hiring laid off oil workers.

Last month, California pledged that every new passenger car and truck sold in the state in 2035 will be a net-zero vehicle that runs without gas. GMC has fashioned the Hummer, one of the greediest gas hogs on the road, into an all-electric vehicle.

Oil industry representatives begged to differ, saying it will continue to dominate the energy sector for years to come, regardless of who is president. “We aren’t going anywhere,” said Mike Sommers, head of the American Petroleum Institute.

However, the industry is starting to change. London-based British Petroleum, one of the world’s largest oil and gas companies, announced in August that it plans to dramatically cut back its oil and gas business. And five of the six largest U.S. banks — Citigroup, Goldman Sachs Group, JPMorgan Chase, Morgan Stanley and Wells Fargo — have pledged in the past year to stop funding new drilling and exploration in the Arctic.

Despite these factors, Biden’s carbon pollution reduction goals remain a hard sell to many. The past few days have shown that it’s not just Republicans in that camp.

“It’s not realistic,” said Horn. “It’s just not.”

Felicia Sonmez and Will Englund contributed to this report.