Spurred by dire scientific warnings and new Capitol Hill protests, Democrats preparing to run for president have been rushing to shift their plans for combating climate change, highlighting an issue once considered a political liability, especially in Midwestern swing states won by President Trump.

Aides to a half-dozen senators considering a 2020 campaign met with supporters of the Green New Deal, an effort pushed by Rep.-elect Alexandria Ocasio-
Cortez (D-N.Y.) that could turn into a litmus test for Democratic candidates, organizers said. Other potential candidates are weighing activist demands to swear off donations from the political action committees or executives of companies involved in fossil fuel production.

At least three potential candidates, Washington Gov. Jay Inslee (D), Sen. Bernie Sanders (I-Vt.) and Sen. Jeff Merkley (D-Ore.) have made clear that if they run, they intend to make climate change a central campaign issue.

“It just simply has to move into the front tier. It has to become a primary force of our economic growth policy,” Inslee said in an interview, one day after announcing ambitious carbon-reduction goals for his state this past week.

Merkley said he would introduce his own version of a Green New Deal proposal next year. “We absolutely have to make sure this is part of the conversation going into 2020,” he said. “Mother Nature is sending this message, and the youth have doubled down on the message.”

At the core of the push is a broader effort by some party leaders to reframe the political debate over climate away from policies that would impose new costs on carbon pollution — through taxes or a cap-and-trade program — toward a focus on investing in energy conservation and efficiency as a way to spark economic development, especially in economically depressed areas.

This rejection of the last major Democratic push for economywide climate legislation in 2009 is the premise of the Green New Deal proposal that House Democrats have been steadily embracing in recent weeks. It has been presented as an alternative to legislation focused on imposing a carbon tax and then refunding the money to households in the form of checks, a move that would most benefit lower- and middle-class households because of the progressive tax code.

“Given the magnitude of the current challenge, the tools of regulation and taxation, used in isolation, will not be enough to quickly and smoothly accomplish the transformation that we need to see,” reads the draft proposal posted on Ocasio-Cortez’s website.

The proposal instead calls for a special committee in the House to draft a plan by 2020 for a historic multitrillion-dollar federal spending and loan program with the goal of building a “100 percent greenhouse gas neutral power generation system” and providing millions of jobs in low-income areas. The plan recently gained the support of the incoming chairman of the House Rules Committee, Rep. Jim McGovern (D-Mass.), and the co-chairs of the Congressional Progressive Caucus.

Given Republican control of the Senate and likely opposition by President Trump, there is little expectation that the effort will pass into law before the upcoming presidential election, though organizers hope it will shape the debate in the interim.

“There is no doubt that there has been some movement now that [congressional] offices are being occupied,” said Sean McElwee, a co-founder of Data for Progress, a group that drafted an early version of the Green New Deal in September. “The reason offices are being occupied is because for a long time it seemed like we were heading into the 2020 presidential primary with no one talking about this.”

Recent natural disasters and new research have also lent urgency to the conversation and expanded its audience. A federal National Climate Assessment released last month found that climate change would cause dramatic harm to every region of the country, costing billions of dollars from increasingly debilitating hurricanes, droughts, wildfires, heat waves and floods. Another recent report from the United Nations found that the world has only a dozen years to take drastic action to respond to the threat.

Climate negotiators from around the world struck a deal Saturday in Poland that keeps the world moving forward with plans to curb carbon emissions, but the Trump administration says it plans to withdraw the United States from the process, which was agreed to in Paris in 2015 and is designed to have nearly 200 countries cut their production of greenhouse gases.

Sanders, who previously endorsed a large carbon-tax plan, has said he will announce a plan next year to create millions of jobs as part of an effort to combat climate change.

“The U.N. report made clear that the timeline we have to avoid the worst impacts of climate change is just different from the timeline people were thinking about in years past, so rethinking these policies is something everyone should be thinking about,” said Ari Rabin-Havt, a Sanders adviser. “The conversation has moved to this concept of the Green New Deal.”

Young climate activists say that simply signing on to ambitious policy proposals will not be enough. Organizers of the Sunrise Movement, the group that has been staging climate protests at the Capitol, plan to demand that Democratic 2020 candidates take a further step of promising to refuse campaign donations from executives and political committees of fossil fuel companies.

Merkley joined Sanders this past week as the second potential presidential contender to have signed on to the pledge.

“If any of them want to be taken seriously by our generation, they need to show they are willing to stand up to the fossil fuel polluters who have stalled action on climate change our whole life,” said Stephen O’Hanlon, a spokesman for the Sunrise Movement. “In 2019 we are going to be putting pressure on all of them.”

He said the group has been meeting with representatives of Sens. Cory Booker (D-N.J.), Kamala D. Harris (D-Calif.), Kirsten Gillibrand (D-N.Y.), Elizabeth Warren (D-Mass.), Merkley and Sanders — all of whom are pondering presidential runs.

“We’ve been supportive of the goals of the Green New Deal,” said Lily Adams, a spokeswoman for Harris.

The failure of a November statewide ballot effort to tax carbon in Washington state and the recent protests over a new fuel tax in France have shown the continued political challenge of addressing climate change.

Rep. John Delaney (D-Md.), the only declared congressional Democrat running for president, has said politicians still need to lead with market-based solutions such as a carbon tax, while emphasizing that the “dividends” from new taxes will be distributed back to the public.

“Whatever approach you take, it will inevitably be a big jobs program,” he said of a recent ­carbon-tax bill he introduced in the House.

But climate-change solutions could create problems for Democrats in Midwestern states that continue to rely heavily on fossil fuels for electricity generation and jobs. Trump, who has repeatedly denied the climate threat and boosted the fossil fuel industry, has made clear the promotion of oil, natural gas and coal is likely to be a major part of his reelection effort.

Sen. Sherrod Brown (D-Ohio), a potential presidential candidate, boasted during his 2012 campaign about his support for “coal jobs,” the recent growth in coal production in the state and his efforts to resist new regulations on coal power plants. President Barack Obama also supported “clean coal” during his 2008 election campaign and backed an “all-of-the-above” energy strategy in 2012.

Brown was one of several Democrats who expressed concern in 2009 about the House-passed effort to impose a cap-and-trade system that would have put a price on carbon emissions, though he has supported raising fuel-economy standards, preserving Obama’s “Clean Power” regulations and providing tax credits for wind, ­solar and biofuel generation.

“I’ve never bought that you play off workers against the environment, because what I have seen is good environmental policy means more good jobs,” he said recently on Pod Save America, a liberal podcast, when he was asked about the Green New Deal. He said he did not know enough about the particulars of the proposal to take a position on it.

Tom Steyer, an investor and environmental activist who is also considering a presidential campaign, has argued that the worst thing Democrats can do to tackle climate change is to push top-down solutions such as a carbon tax. His recently released five-point political platform makes no mention of the warming planet, referring instead to clean air and water and a living wage.

“The only way to win on energy is to talk about justice,” Steyer said in a recent interview. “You can’t talk about climate. You have got to talk about jobs and health. This has to be simply related to human beings.”

In the House, the new approach marks a return to the idea that federally subsidized green jobs could be a primary way of rehabilitating economically depressed areas of the country. The idea was floated in the run-up to the 2008 election and became a central part of the 2009 stimulus plan championed by Obama. Many activists now pushing the idea, including Ocasio-Cortez, were teenagers at the time.

Van Jones, a former Obama administration official, recently presented Ocasio-Cortez with a copy of his 2008 book “The Green Collar Economy,” which argued that climate change would lead to an employment boom in depressed areas. Jones used the term “green new deal” as far back as 2008.

“She wasn’t aware that I had written the book. The idea’s time has come,” said Jones, who now hosts a show on CNN.

Steven Mufson contributed to this report.