Hillary Clinton has started to roll out what her campaign calls an ambitious agenda to tackle the threat of global warming.
But she still refuses to take a stand on the controversial Keystone XL pipeline.
The pipeline, which has been under review by the administration for more than six years, has become a flashpoint in a contentious national debate over global warming and the future of American energy security. Environmentalists oppose the project and view Clinton's silence as frustrating and alarming.
At an event in Iowa on Monday, Clinton was asked by a reporter if she would take a position on the pipeline now that she has officially entered the race as a 2016 White House contender.
Clinton sidestepped the question by saying that the State Department review of the pipeline should be allowed to play out, suggesting that her tenure as secretary of State when the review began disqualified her from weighing in.
"I will refrain from commenting because I had a leading role in getting that process started and I think that we have to let it run its course," Clinton said, adding that she is confident that Keystone's impact on global warming will be "a major factor" in the administration's determination of whether or not the pipeline is in the national interest.
Since leaving the State Department, Clinton has repeatedly declined to say if she thinks the pipeline should be built. But now that her campaign has started to outline an official climate agenda, environmentalists are hoping that the 2016 Democratic front-runner will break her silence.
Martin O'Malley and Bernie Sanders, Clinton's Democratic opponents on the Left, both vocally oppose the construction of the pipeline. But weighing in on Keystone would put Clinton in a tough spot. Environmentalists protest the project but labor unions, a major source of Democratic backing, say that its construction would create jobs. For now, Clinton looks intent on keeping quiet.
The Clinton campaign outlined a series of first steps to ramp up renewable energy on Sunday evening and rolled out a video in which Clinton warned that action must be taken now to fight back against the problem of Earth's rapidly rising temperatures.
That announcement avoided any mention of the pipeline as well as other controversial issues, such as whether Clinton would support drilling off the Arctic coast.
Bill McKibben, the founder of grassroots environmental group 350.org, called on Clinton to say what she thinks about Keystone on Monday before her remarks in Iowa.
"Now, we need Clinton to show she understands the other half of the climate-change equation—and prove she has the courage to stand up against fossil fuel projects like offshore and Arctic drilling, coal leasing in the Powder River basin, and the Keystone XL pipeline."
Clinton indicated that she would build on President Obama's use of executive action to fight climate change, but added that she believes she may also be able to convince Congress to work with her.
"We still have a lot [that we can do] without getting congressional support," Clinton said, adding: "Making this a central issue in my campaign, I hope, will give me the momentum to be able to go to the Congress and say look, cease fire. We need to make the transition, and we can do it and save money at the same time, and create millions of new jobs and businesses that will be to the benefit of our country.
"As president, I'll do everything I can to lead us toward that clean-energy future," Clinton said.
This story is breaking and has been updated.