But that hasn’t convinced the environmental lobby’s heavy hitters to cut checks for Landrieu. In the past year, only one environmental organization has donated to her campaign. The Baton Rouge-based Center for Coastal Conservation gave Landrieu a $2,500 nod, according to the Center for Responsive Politics. The Sierra Club, Natural Resources Defense Council, and Environmental Defense Fund have handed over a combined contribution of exactly nothing. All three groups declined to comment on the record when asked whether they would endorse Landrieu.

So why have environmentalists thus far washed their hands of a campaign so critical to their movement’s future?

In short: They just can’t stand her stance on global warming. Landrieu is an oil- and gas-industry champion who tiptoes around the global-warming debate and voted to block the Obama administration’s climate rules for power plants. Lining up behind a candidate like that, environmental groups fear, would signal to Democrats that their support is unconditional—and that greens can be taken for granted.

“We don’t want to be in a situation where one party feels like we’re beholden to them. That’s how we get taken advantage of,” said Ben Schreiber, a spokesman for Friends of the Earth Action, the political fundraising arm of Friends of the Earth. “Candidates need to know that there are consequences to the way they vote.”