Hillary Clinton knows a thing or two about the Keystone XL pipeline, but good luck trying to get her to give her opinion publicly.
She led President Obama's State Department while it endlessly scrutinized the project and once declared she was "inclined" to sign off on the pipeline. Bill Clinton has said Americans need to "embrace" the pipeline. And it's an issue near and dear to the hearts of major Democratic donors critical to her 2016 presidential plans.
But Clinton now refuses to say what she thinks about the pipeline that has ignited a contentious debate over global warming and American energy security.
Her silence frustrates environmentalists who want assurances that Clinton is on their side. But Washington's green power players have stopped short of publicly pressuring her into taking a stand, and high-profile environmentalists say it won't make much difference if Clinton breaks her silence at all.
"Of course I wish she would say something, but I don't go to bed at night worrying that Hillary Clinton isn't talking about Keystone," said Bill McKibben, the founder of grassroots environmental group 350.org, which helped elevate the issue in Democratic circles.
The latest twist in the years-long saga over Keystone arrived Tuesday when Obama vetoed legislation to approve the pipeline, a rebuke to Republicans who campaigned on the issue in 2012 and 2014.
But Obama's veto did not elicit a reaction from Clinton. She didn't mention the project Tuesday when she spoke at Lead On, the women's leadership conference in Silicon Valley.
Clinton has declared that she will not comment on the project until the administration's review wraps up. "You won't get me to talk about Keystone because I have steadily made clear that I'm not going to express an opinion," she said in Canada last month.
Environmentalists warn that the $8 billion pipeline, which would haul heavy crude from Canada to the Gulf Coast, would worsen global warming. And many hope that Clinton might break her silence when Obama makes a determination on the project, an announcement that could arrive in the coming weeks. But green groups inside the Beltway are hesitant to expend political capital on the issue for now.
Electorally minded environmentalists are averse to pressuring Clinton on the pipeline before she formally announces a bid for the Oval Office and as long as a final decision rests with Obama. Their reluctance is an indicator that while Washington environmentalists recognize that opposition to the pipeline has become a powerful rallying cry, they are far more concerned with whether Clinton plans to make climate change a key plank of her political platform.
"Obama is the decision-maker on this so it's less important if Clinton weighs in," said Lena Moffitt, National Wildlife Federation's senior climate and energy program manager. "We're not going to make this a litmus test, but we do want to make sure that Clinton recognizes that climate change must be a central consideration for any major infrastructure or energy project."
Green groups are also optimistic that Clinton is already on their side, a conviction bolstered by the expectation that John Podesta, a former senior advisor to Obama credited with pushing green priorities and an outspoken opponent of Keystone, will counsel Clinton on a presidential run.
"We certainly are huge fans of both Secretary Clinton and John Podesta and both have a long history of tackling climate change. So with the two of them working together, it's hard to imagine that she would not run as an environmental champion," said Tiernan Sittenfeld, the League of Conservation Voters' senior vice president for government affairs.
That certainty is not universal. Grassroots environmental groups like 350.org and Friends of the Earth are skeptical of Clinton's green record, partly because she has voiced cautious support for fracking, the technology enabling America's natural gas boom.
Reports last week that the Clinton Foundation has taken in millions of dollars in donations from major oil and gas companies, including ExxonMobil, and a Canadian trade agency promoting construction of Keystone sparked concern in environmental circles.
And if Clinton so much as hints at support for the pipeline, let alone declares her love for Keystone, environmentalists would be furious.
The pipeline puts Clinton in a tough spot. Adamant opposition would leave her open to criticism from congressional Republicans who support the project, as well as labor unions, a key Democratic constituency.
"Keystone is an important infrastructure project that's shovel-ready," Senate Majority Leader Mitch McConnell said on the Senate floor Tuesday. "It would pump billions into our economy."
While serving as secretary of State in 2010, Clinton's comments that the department was "inclined" to green-light the pipeline drew sharp criticism from environmentalists.
Clinton's 2010 statement cited energy independence concerns. "We're either going to be dependent on dirty oil from the Gulf or dirty oil from Canada," Clinton said at the time, although she added a call to invest in renewables as well.
"She basically said she would approve the project when she was at State. So there's a lot of trust there that would need to be rebuilt," said Ben Schreiber, Friends of the Earth's climate and energy program director.
And while progressive environmentalists still want to see Clinton decry Keystone, grassroots leaders say that even the boldest of declarations against the pipeline would not be enough to prove pure intentions.
"I'm certainly not holding my breath," McKibben said. "I think she has a lot of ground to make up to get enthusiastic support from the environmental world. While Keystone is an important issue it's one of dozens and she hasn't been out front on any of them."
350.org and Friends of the Earth, along with other progressive environmentalists, have also called into question the integrity of the State Department review of the project, a process that Clinton oversaw.
But that doesn't mean that environmentalists won't press Clinton for her opinion on Keystone when a final decision arrives.
Bold Nebraska, a left-leaning nonprofit that has become a major player in the pipeline fight, plans to pressure Clinton to take a stand on Keystone once Obama makes up his mind. And other green groups could join in.
"We understand why she doesn't want to get ahead of the president so we'll give her a pass on that," said Bold Nebraska director Jane Kleeb, "but as soon as the president makes that decision, she is going to have to address this issue."
This story has been updated with additional information.