Hillary Clinton has hired a former lobbyist for the company behind the Keystone XL pipeline, further upsetting environmentalists who have long been wary of her commitment to fighting climate change.

BuzzFeed’s Ben Smith reported on Wednesday that the Clinton campaign has hired Jeffrey Berman as a campaign consultant. Berman, who began working for the campaign earlier this month, once lobbied on behalf of TransCanada, the company that hopes to build a pipeline carrying tar sands oil from Canada to the southern coast of the U.S. 

R.L. Miller of Climate Hawks Vote said Berman's hiring "is a disappointment—especially as Martin O'Malley is taking flight based on the best climate plan I've seen from a candidate, and Bernie Sanders continues to soar."

"For us it’s a signal that she continues to be willing to work with oil and gas interests and take money from folks who are committed to have a pathway to fossil fuels," said Ben Schreiber, Friends of the Earth's climate and energy program director.

In 2008, political operatives described Berman as an “unsung hero” of Obama’s upset win over Clinton, due to a strategy that won Obama more delegates in key primaries when Clinton was still ahead in the popular vote. After Obama’s win, Berman joined the lobbying firm Bryan Cave LLC, which retained TransCanada as a client until 2013.

Federal disclosures show that TransCanada paid Bryan Cave $120,000 to lobby the State Department—to “monitor climate change legislation and presidential permit process for TransCanada Keystone Pipeline,” per the disclosure form—while Clinton was secretary. Berman is listed as the lobbyist on this issue.

In 2010, Clinton said she was "inclined" to approve a permit for the pipeline. She's refused to take a position ever since. “I have steadily made clear that I'm not going to express an opinion” she said in January, which also happened to be the same week the Senate considered a bill to fast-track the six-year-long delay to a permit. Clinton’s extended network has other connections to TransCanada, like her 2008 national deputy campaign manager Paul Elliot, now an in-house lobbyist for TransCanada. And the Wall Street Journal reported in February that between Clinton's tenure at the State Department and campaign for president, the Clinton Foundation received millions of dollars in donations from ExxonMobil and nearly half a million dollars from Canada's Foreign Affairs, Trade and Management agency, which supports the pipeline. 

Even though Clinton has made early promises to take an aggressive stand on climate change, environmental groups remain wary. Friends of the Earth has requested public records from the State Department on Bryan Cave's lobbying during Clinton's tenure. Still, the bulk of the environmental campaign community is reluctant to criticize the likely Democratic nominee outright. It's unclear whether these donations and distant connections ever represented a conflict of interest for Clinton, and Democratic donor and climate activist Tom Steyer continues to hold fundraisers for Clinton regardless of the criticism. 

Clinton's opponents still sense an opportunity to outdo the frontrunner on climate change. Former Maryland Governor Martin O’Malley received positive reviews from Steyer and other activists last week for proposing that the U.S. adopt 100 percent clean energy by 2050. And Vermont's Bernie Sanders already is a favorite among green activists for championing climate legislation in the Senate. 

What does Clinton need to do to convince environmentalists she's on their side? Her critics argue she needs to come out with an aggressive and detailed plan to cut greenhouse gas emissions in the next 35 years.

"Hiring as a high-ranking campaign official someone who spent years on TransCanada's payroll lobbying for Keystone is a big step in precisely the wrong direction," a spokesperson for 350 Action said. "We need bold ideas and leadership from our candidates—like a plan to decarbonize the United States by 2050, not a campaign that says nice things about renewable energy while letting Big Oil's lobbyists and cronies drive the bus."

"The best thing Clinton could do for her campaign to bolster her climate credentials," said Climate Hawks Vote's Miller, "is an honest and lengthy interview on the subject of Keystone XL, in which she describes all the steps taken at the State Department that appeared to nudge it forward while maintaining a semblance of neutrality, and the reason she's now deciding to say no to one of the dirtiest and notorious projects of the decade."