President Trump needed just five days in office to begin trying to reverse both decisions.
When Obama announced in November 2015 that he was rejecting Keystone XL, which would have transported oil from Canada's tar sands to an existing pipeline in the United States, international meetings that would lead to the historic Paris climate accord were just weeks away. The former president made clear that he was concerned about his environmental legacy and the world's future.
"America is now a global leader when it comes to taking serious action to fight climate change," Obama said at the time. "And, frankly, approving this project would have undercut that global leadership."
When Trump announced his executive actions on Tuesday to try to revive the Keystone XL pipeline, which would extend from northern Alberta to Nebraska, as well as the Dakota Access pipeline, which would run through North Dakota, South Dakota, Iowa and Illinois, there was no talk of climate change or global environmental leadership.
Among his motives, he told reporters: "a lot of jobs."
How momentous either president's decision was is open to debate. Both the economic and environmental impacts have been greatly overstated at times. Experts note that individual pipeline projects rarely create many long-term jobs. Nor, as standalone projects, do they significantly increase or limit climate change.
Yet both men understand the power of symbolism, and Trump's moves Tuesday made it clear that the days are over when administration officials weighed whether a domestic energy project serves the greater global environmental good. Trump's orders said loudly: "America first."
"I believe that construction and operation of lawfully permitted pipeline infrastructure serve the national interest," Trump wrote in a memorandum directing the U.S. Army Corps of Engineers to consider granting the final permit for completion of the $3.8-billion, 1,170-mile Dakota Access pipeline.
Among the problems with Trump casting Keystone XL as a project in service of America's interests is the fact that it has been proposed by a Canadian company, TransCanada. It would transport Canadian oil into and through the United States, some of it to be exported overseas.
Trump nodded to this by directing the secretary of Commerce to make sure that all major new pipeline projects "use materials and equipment produced in the United States, to the maximum extent possible and to the extent permitted by law."
The use of American steel had come up on Monday, when Trump met with several manufacturing and trade union leaders. On Tuesday, some of those groups praised Trump's orders on the pipelines though they said they were unsure what would happen next. They, too, described the moves in terms of American jobs, not Canadian oil or global climate change.
"To us, this is a clear symbol that America is open for business," said Ross Eisenberg, vice president of energy and resources policy for the National Assn. of Manufacturers. "It is the sign that the manufacturers have been looking for on energy and on everything else."
Native American protesters who have led opposition to the Dakota Access pipeline in North Dakota vowed Tuesday to continue to fight its construction. And while the Canadian government and TransCanada both praised the decision regarding Keystone XL, the pipeline still faces challenges at the state level should TransCanada apply again to build it.
"As soon as they try to, we'll file the same lawsuit," said Jane Kleeb, president of Bold Alliance, an environmental group based in Nebraska, where property owners sued to stop the taking of property for the pipeline by eminent domain.
It is easy to forget that both projects once appeared headed for approval at different points under the Obama administration — and that Obama once boasted of the rate at which his administration had approved pipelines.
But that was before they became an international symbol of fossil fuel extraction and climate change.
Brigham McCown, who led the Pipeline and Hazardous Materials Safety Administration under President George W. Bush, told reporters Tuesday that, although the nation has 2.6 million miles of oil and gas pipelines, more are needed.
"Perhaps we haven't done the best job of explaining why pipelines and other energy infrastructure is necessary," McCown said in a conference call organized by supporters of the Dakota Access pipeline.
Many consumers of gas and electricity still do not understand how it's delivered, McCown said. "I think we have to make folks understand that they can't take this system for granted."