Donald Trump listens as Hillary Clinton answers a question from the audience during the second presidential debate Sunday. (Rick Wilking/Reuters)

The League of Conservation Voters will spend at least $40 million this election, according to its president, Gene Karpinski, a record-setting amount for the group that underscores the extent to which liberal groups are working to buttress Democrats’ campaigns this year.

Coupled with the efforts of billionaire Tom Steyer’s NextGen Climate and a handful of other groups, such as the Environmental Defense Action Fund, the Natural Resources Defense Council Action Fund and the Sierra Club, environmental activists are poised to spend more than $100 million this cycle. Together they spent $85 million in the 2014 elections.

“The stakes have never been higher, and the contrasts have never been starker,” Karpinski said in an interview, where he disclosed his group’s fundraising total for the first time. He said the $40 million in spending is “by far, our biggest investment in a political cycle to date.”

LCV and its affiliates will spend at least $10 million backing Democratic presidential nominee Hillary Clinton and more than $15 million on congressional races — primarily on the Senate contests in Pennsylvania, Nevada and North Carolina. By contrast, the group spent roughly $25 million in 2014, $15 million in 2012 and $5 million in 2010.

While environmentalists’ generous spending in the last election cycle did not translate to a string of victories, they said that this year they were confident that a conservation-focused message could help sway voters in key demographic groups, including millennials, Latinos and African Americans, to back Clinton and other candidates.

The Natural Resources Defense Council Action Fund is spending at least $1 million this election on activities, including ads and direct mailing to its members. In addition, the NRDC Action Fund political action committee has joined with LCV Action Fund and NextGen Climate to raise and contribute at least $7 million for federal and state candidates through two bundling programs, GiveGreen and GiveGreen in the States.

“We think our issues can be particularly potent with the groups that Senate candidates and Clinton need most to bring out, including millennials and minority groups,” said NRDC Action Fund’s director of governmental affairs, David Goldston. “We think it is in those areas our issues have the potential to get to people who otherwise might be less active.”

Both the Environmental Defense Action Fund, which is devoting $5 million, and the Sierra Club, which is spending $3.8 million, are ramping up their election activities this year. And in a recent interview, Steyer said his group would spend at least $55 million this cycle, though it could be much more than that.

Democrats, such as Clinton, will be the primary beneficiaries of environmental groups’ largesse, though both LCV and the Sierra Club backed a Republican running in a North Carolina House primary, Jacob Walser, who lost, and both groups backed some state GOP candidates this year. EDF Action spokeswoman Sharyn Stein said her group is “backing candidates in both parties” in this election, including Rep. Carlos Curbelo (R-Fla.).

Karpinski said that his group’s approach was driven by the candidates’ voting record, noting that the GOP candidates they’re targeting — Sens. Richard Burr (N.C.) and Patrick J. Toomey (Pa.) and Rep. Joseph J. Heck (Nev.) — have lifetime LCV scores of 7 percent, 7 percent and 8 percent respectively. Their Democratic opponents, he said, all have a history of promoting conservation goals.

“In each case, it’s a case of someone who will be great on our issues, and someone who will be terrible on our issues,” he said.

LCV received considerable blowback from supporters of Sen. Bernie Sanders (Vt.) when it decided to endorse Clinton in November, before a single Democratic primary vote was cast. But Karpinski called that “one of the best decisions we’ve ever made,” because it translated into earlier donations from supporters and sped up the group’s organizing efforts on the ground.

An array of liberal advocacy groups are launching massive voter mobilization efforts to boost Clinton and down-ballot Democrats. Together, they could amount to the biggest ground push ever in a presidential campaign. Planned Parenthood Action Fund is rolling out its largest program ever, spending $30 million on voter canvassing, direct mail and digital targeting in Nevada, North Carolina, New Hampshire, Pennsylvania and Ohio. Labor unions are financing their own robust campaigns, augmented with millions from Steyer, who is also spending an additional $25 million through his own super PAC to turn out millennials.

Environmentalists are making one major change in their strategy this election: They are devoting far more time to field organizing rather than advertising. NextGen Climate, which spent millions on the airwaves in 2014, set up operations on 200 college campuses in eight states at least a year ago. And LCV has decided to focus more on persuadable voters than mobilizing those already inclined to back the group’s favorite candidates.

“We’ve moved this cycle to really focus on persuasion,” said Clay Schroers, LCV’s independent expenditure director, adding that analytic testing suggested they should extend their conversations when they knock on doors from under a minute to two or three minutes on average. “We’re trying to extend and deepen the conversations our canvassers have so they’re more memorable to the voters.”

Steyer said in an interview last month that he’s become convinced that establishing a long-term presence on college campuses will do more to advance his group’s environmental agenda than blanketing the airwaves.

“There’ll be a lot of people running TV ads, but it won’t be us,” he said. “The average time people retain a TV ad is seven days.”

Matea Gold contributed to this report.