President Donald Trump signed executive orders on Tuesday to push forward the Keystone XL and Dakota Access pipelines, opening new fronts in his looming war with environmentalists.

Keystone was rejected in 2015 by former President Barack Obama after a seven-year review. Trump’s orders clear the way to continue building Energy Transfer Partners’ 1,172-mile Dakota Access project, which has been stalled since the U.S. Army Corps of Engineers halted construction in December amid massive protests led by the Standing Rock Sioux.

“This is with regard to the construction of the Keystone pipeline, something that has been in dispute, and subject to a renegotiation of terms by us,” Trump said of the first action during a signing broadcast on TV networks Tuesday morning. “We’re going to renegotiate some of the terms and if they would like, we will see if we can get that pipeline built. A lot of jobs, 28,000 jobs. Great construction jobs.”

Trump then signed the second action.

“This is with respect to the construction of the Dakota Access Pipeline,” he said, introducing the leather-bound order. “Again, subject to terms and conditions to be negotiated by us.”

Another action signed Tuesday calls for U.S. steel to be used if the pipelines are built, though that may mean little in the case of the Dakota Access Pipeline, which is nearly complete. One more order aims to overhaul what Trump called the “horrible permitting process” by slashing environmental regulations.

“If we’re going to build pipelines in the United States, the pipelines should be built in the United States,” Trump said. “We’re going to put a lot of workers, a lot of steelworkers back to work. We will build our own pipes, we will build our own pipelines, like we used to in the old days.”

The moves mark the first serious step by the new president to reverse his predecessor’s environmental gains in favor of propping up an oil and gas industry dogged by low prices, competition from renewable energy and regulations aimed at cutting carbon emissions. Republicans, who pushed Obama to greenlight both pipelines, hailed the orders as a victory.

“The unfortunate reality is that these important infrastructure projects were used by special interests to advance their radical anti-energy agenda and were therefore needlessly halted by the last administration—to the detriment of America’s national interest,” House Speaker Paul Ryan (R-Wis.) said. “These pipelines will strengthen our nation’s energy supply and help keep energy costs low for American families.”

The day after Trump’s surprise election victory, TransCanada, the company behind the Keystone XL, announced plans to meet with the incoming administration to once again pitch the proposed 1,179-mile oil conduit from Alberta to Nebraska. The firm said Tuesday it was preparing an application to submit.

Trump said in May he would support the Keystone pipeline if the U.S. government could get a share of its revenue, which may not be legal. But Trump’s vow to renegotiate the 1993 North American Free Trade Agreement, on which he plans to sign an executive order this week, could complicate things. In June, TransCanada sued the U.S. government through a legal clause in NAFTA.

Still, Keystone XL may prove easier than the Dakota Access Pipeline to build ― the State Department handles large parts of the permitting process because the conduit crosses a border, Daniel Riesel, senior partner at the environmental law firm Sive, Paget & Riesel, told The Huffington Post.

The pipeline would largely pump oil from tar sands ― a noxious mix of sand, clay and bitumen, a thick, viscous oil ― to refineries on the Gulf coast of Texas. Keystone XL would carry 830,000 barrels of tar sand oil, considered one of the dirtiest fossil fuels, into the U.S. daily, producing emissions equivalent to putting 5.6 million new cars on the road, according to estimates by the environmental nonprofit Friends of the Earth.

The Washington Post via Getty Images A map shows where the Keystone XL, an extension of the existing Keystone pipeline, would run.

The project, which drew opposition from a broad coalition of conservation and climate advocates, would likely renew lawsuits and protests to stop construction.

“This is not a done deal,” Bill McKibben, co-founder of the environmenalist group 350.org, said in a statement. “The last time around, TransCanada was so confident they literally mowed the strip where they planned to build the pipeline, before people power stopped them. People will mobilize again.”

The Dakota Access Pipeline may face less intense resistance. Protesters hailed victory in December when the Army denied a permit for the $3.8 billion project to build under North Dakota’s Lake Oahe, a sacred body of water to the Native American tribes who live there. The pipeline, meant to carry crude from the Bakken oil field, is mostly complete, save for a stretch near the Standing Rock Sioux reservation. Even as temperatures in the massive protest camp near the dig site fell below zero, legions of protesters ― including 2,000 veterans who came to serve as “human shields” ― remained.

But on Friday, Standing Rock leaders asked protesters to decamp as the tribe plans to continue its fight against the pipeline in the courts. The protesters, who called themselves “water protectors,” have until Jan. 30 to leave the main camp, according to a resolution unanimously passed by the Standing Rock Sioux Tribal Council in Fort Yates, North Dakota.

“Moving forward, our ultimate objective is best served by our elected officials, navigating strategically through the administrative and legal processes,” the Standing Rock Sioux Tribe said in a statement posted to Facebook, where the hashtag #NoDAPL went viral over the summer. “For this reason, we ask the protectors to vacate the camps and head home with our most heartfelt thanks.”

Creating a second Flint does not make America great again. Dave Archambault II, chairman of the Standing Rock Sioux Tribe

Soon after Trump signed the orders, Earthjustice, the legal nonprofit representing the Standing Rock Sioux in court, vowed to challenge the actions. The group noted that Trump used to own a stake in the pipeline’s developer. Though Trump sold the stake in December, Earthjustice believes it could still provide a means to fight the pipeline on ethics grounds.

“This move is legally questionable, at best,” Earthjustice President Trip Van Noppen said in a statement. “[Trump] should brace himself to contend with the laws he is flouting, and the millions of Americans who are opposed to these dangerous and destructive projects. We will see his administration in court.”

The order on the Dakota Access Pipeline actually qualifies as a memorandum directing the Army to complete the permitting process as quickly as legally possible. The law already requires the Army to conduct a fully environmental analysis and consider alternative routes, the group said.

“The Army may respond to this order by issuing the easement within the next few days, at which time construction would likely begin again,” Earthjustice spokesman Phillip Ellis wrote in an email to HuffPost. “Alternatively, the consideration directed by this Memorandum could take longer. We just don’t know at this point.”

The existing pipeline route risks contaminating water used by the tribe and by 17 million Americans downstream, said Dave Archambault II, chairman of the Standing Rock Sioux Tribe.

“We are not opposed to energy independence. We are opposed to reckless and politically motivated development projects, like DAPL, that ignore our treaty rights and risk our water,” he said.

Archambault then alluded to the lead-tainted water crisis in Flint, Michigan, saying, “Creating a second Flint does not make America great again.”

On Monday, with almost eerie timing, a pipeline in the western Canadian province of Saskatchewan leaked 52,834 gallons of oil on tribal lands, precisely illustrating the fears of protesters on the U.S. side of the border.

“Millions of people came together all over this country to stop the Keystone XL and Dakota Access pipelines and say we must transform our energy system away from fossil fuels to renewable energy,” Sen. Bernie Sanders (I-Vt.), who asked Trump’s Cabinet nominees some of the toughest climate questions during last week’s confirmation hearings, said Tuesday in a statement. “Today, President Trump ignored the voices of millions and put the short-term profits of the fossil fuel industry ahead of the future of our planet.”

Trump, who has incorrectly described climate change as a hoax invented by the Chinese, laid out a vision to kick-start the U.S. economy by slashing environmental regulations and boosting the oil, gas and coal industries. He has stacked his Cabinet with fossil fuel allies and climate science deniers, including in key positions that affect the environment.

During the first White House briefing in which he took questions from the press, press secretary Sean Spicer dodged a question from HuffPost on Monday about how Trump plans to address the fact that scientists say climate change is close to harming human civilization, given that 2016 was the hottest year on record.

“He’s going to meet with his team and figure out what policies are best for the environment,” Spicer said. “One of the things he talked about during the campaign is there’s a balance, and he’s trying to make sure we use our resources appropriately, that we maximize things to make sure that we don’t do so at the detriment of economic growth and job creation.”

Trump’s bet on dirty energy comes as China, the world’s biggest polluter, cancels plans for 103 new coal-fired power plants and urges Trump not to pull out of the historic climate accord reached in Paris in 2015.

“While countries like China and Germany continue to make progress in their transition away from the dirty energy of the past, this action will roll back the progress we have made,” Sen. Brian Schatz (D-Hawaii) said in a statement.

“Climate change is the challenge of our generation, and we need to be moving forward with policies to support clean energy,” Schatz went on. “The Keystone XL and Dakota Access pipelines are simply not in our national interest.”

This article has been updated.