A Democratic fundraiser last week at billionaire Tom Steyer’s home amounted to a summit between Washington’s liberal elite and San Francisco’s climate intelligentsia.

Senate Majority Leader Harry M. Reid (D-Nev.), six other senators and a 2014 Senate candidate took in views of the Golden Gate Bridge with former vice president Al Gore and some of the nation’s richest environmentalist donors.

The $400,000 fundraiser, held for the Democratic Senatorial Campaign Committee, included remarks from Gore, who said the party needs to make global warming a central issue during the midterms, participants said. And Gore called Steyer, who has vowed to raise at least $100 million,“Mr. Tipping Point.”

“How do you inject this into the debate in a meaningful way?” Steyer said in an interview during a visit last week to Washington, where he lobbied a gathering of Democratic governors. “That changes what can happen in Washington D.C.”

With the end of President Obama’s tenure now in sight, wealthy environmentalists are pushing Democrats to take bolder positions on climate change — vowing to emphasize the issue in swing-state contests and threatening to withhold money from candidates who support the Keystone XL oil pipeline.

In the Senate, Reid has pledged to allot time to anyone who wants to discuss climate change during weekly party lunches or on the Senate floor. Sen. Barbara Boxer (D-Calif.) is laying plans for an all-night talkathon on the subject.

“What was really energizing is everyone understood clean energy would be at the forefront of the Senate agenda,” Wade Randlett, a renewable energy entrepreneur who co-hosted the San Francisco fundraiser, wrote in an e-mail. “It wasn’t back-away; it was clearly lean-in.”

But the Democratic Party’s relationship with the environmental movement remains fraught — torn between fervent believers and centrists reluctant to go against traditional energy industry interests that play a major role in their state’s economies. Most of the Democratic candidates facing the toughest Senate races at the moment are in states that traditionally favor the fossil fuel industry, including Alaska, Louisiana, Kentucky and West Virginia.

Republicans argue that the issue is a losing one for Democrats, who will be seen as siding with environmental extremists. In Kentucky, the U.S. Chamber of Commerce has run ads touting how Senate Minority Leader Mitch McConnell (R) is “fighting back, fighting hard” against EPA rules limiting carbon emissions.

And in Alaska, Americans for Prosperity, a prominent conservative group, announced Friday that it will start airing a statewide TV ad criticizing Sen. Mark Begich (D) for supporting a carbon tax.

Rob Collins, executive director of the National Republican Senatorial Committee, said Democrats will regret giving climate activists an outsized role in the elections.

“Extremism in general-election politics is always a dangerous thing, especially when it’s in the hands of a small group of people with a lot of money,” Collins said, adding that donors are less politically experienced than party operatives.

Steyer’s advocacy group, NextGen Political Action, plans to spend at least $50 million of the former hedge-fund manager’s money, plus another $50 million raised from other donors. The group will refuse to spend money on behalf of Democrats who oppose climate regulation, but will not spend money against them either, according to Chris Lehane, a Steyer consultant.

The National Association of Manufacturers, which is part of a broad coalition challenging federal greenhouse gas regulations, plans to target centrist voters in certain regions to highlight the impact these rules have on small businesses and families.

“You can get down to Zip codes where you have facilities that are closed down or shuttering due to regulation,” said Ned Monroe, the group’s senior vice president of external relations.

In the 2012 election, Monroe said, Mitt Romney expanded the GOP’s vote margin in 11 out of 13 coal counties compared to John McCain’s showing in 2008.

Joel Benenson, who has done polling on energy and environmental questions for Steyer, environmental groups and Obama, said he generally sees tackling global warming as an asset for Democrats. But he agreed there will be “geographic differences” because of where the coal industry remains strong.

Collins acknowledged that Republicans also need to be careful in how they frame environmental issues. “If you talk about the environment and you’re inarticulate, can really turn off key parts of the electorate,” he said.

Democrats believe that some of their best opportunities lie in taking advantage of statements from Republicans who question the scientific consensus on global warming, especially if the candidate also opposes abortion rights and gay marriage.

When it is paired with those other two social questions, Benenson said, climate change is “an issue that becomes one of potency for Democrats.”

In the long term, Benenson added, the issue will bolster the party’s position because younger voters view global warming as more urgent. A year ago he conducted a poll for the League of Conservation Voters that found 70 percent of voters under 40 support “the president taking significant steps to address climate change now” compared to 62 percent of voters over 40.

“There’s a real generational divide that’s in play,” he said. “The trend on this issue is that it’s becoming a more intense issue year by year.”

But climate change still lags in terms of voter priorities. In a January 2014 survey by Pew Research, the issue ranked second-to-last among 20 tested, with a rating of 29 percent.

MWR Strategies president Michael McKenna, a Republican who has worked for industry groups, said he has not seen a shift in people’s willingness to take on the issue and pay money to curb carbon emissions.

“If the economy was growing at 5 percent a year, we’d be having a very different conversation,” he said. “Whatever the great big thinkers on the Democratic side are seeing, I just don’t see.”

Esprit co-founder Susie Tompkins Buell, who attended the San Francisco event, has supported the pro-Obama Organizing For Action (OFA) group and is also a close ally of Hillary Clinton. She wrote in an e-mail that she has lost patience with some in her party.

“OFA has helped put climate deniers on defense and it has played a role in securing EPA regulations of coal, but it has not provided the kind of inspired leadership we need to tackle climate change,” she wrote. “We want to make it perfectly clear to Democratic candidates that we expect them to lead on this issue.”