The Prime Minister's Office reacted swiftly Wednesday to a letter signed by Nobel laureates, including Jimmy Carter, urging President Barack Obama to reject the pipeline.
Carter is the first former president to come out against Keystone XL.
Prime Minister Stephen Harper's office responded with a warning: Remember 1979.
It was a reference to the dip in oil supply which followed the Iranian revolution and touched off a global panic. Prices spiked and long lines formed at gas stations, helping destabilize Carter's one-term presidency.
"Mr. Carter knows from his time as president during the 1979 energy crisis there are benefits to having access to oil from stable, secure partners like Canada," the PMO said.
The statement also cited multiple reviews by the U.S. State Department, which said the project would create thousands of construction jobs without an impact on the environment.
It was during the 1979 crisis that Carter delivered a memorable televised speech — the so-called "Malaise" address.
He asked Americans to avoid unnecessary trips, use carpools and public transit whenever necessary, follow the speed limit, and lower their thermostats. He called energy conservation "an act of patriotism," one that would help the poorest Americans cope with the price shock.
Ronald Reagan was elected president less than 16 months later.
One environmental economist isn't sold, however, on the comparisons to 1979.
"I think it's a little bit of a stretch to say that KXL would buffer the U.S. against a repeat of the oil crises," said Andrew Leach, a professor at the University of Alberta.
"I don't think our government would want to commit to selling oil to the U.S. at below market prices. We don't have a nationalized oil industry, so suggesting we could co-ordinate, at a national level, selling oil at a discount might raise concerns about energy policies of the 1980s era."
In his famous speech, Carter also stressed the need to become more energy self-reliant — by building pipelines when possible and tapping the nation's abundant shale resources.
The 39th president is now lending his voice to a new crisis: climate change.
The letter from the Nobel winners released Wednesday warned Obama that the pipeline issue is key to his legacy.
"You stand on the brink of making a choice that will define your legacy on one of the greatest challenges humanity has ever faced — climate change," says the letter, also signed by nine other Nobel laureates, including South African archbishop Desmond Tutu.
"As you deliberate the Keystone XL tarsands pipeline, you are poised to make a decision that will signal either a dangerous commitment to the status quo, or bold leadership that will inspire millions counting on you to do the right thing for our shared climate."
Obama has signalled that a decision on the Alberta-to-Texas pipeline will come before summer.
He's being squeezed on the issue by factions in his own party. The president is caught between wealthy anti-Keystone donors and pro-Keystone lawmakers at risk of losing their seats in more conservative areas in this fall's midterm elections.
The stakes in that congressional election could be huge. Nearly half the Supreme Court — four out of nine justices — is older than 75 and the party that controls the Senate might gain the upper hand in reshaping the American judiciary for years to come. High-court nominees must be approved by that chamber.
Until now, other former presidents had expressed support for Keystone XL. George W. Bush told an energy conference in Pittsburgh last year: "Build the damned thing." Bill Clinton has urged people to "embrace" the project, albeit under strict precautions.
In Canada, domestic opponents of the Harper government said the little dig at Carter was typical of an approach to politics. The NDP said it's that tendency to poke environmentalists in the eye, rather than work constructively on climate change, that inflamed opposition to pipelines.
"It doesn't surprise me that they would try to take a run at Jimmy Carter who has, I think, enormous credibility in Canada," said the NDP's Peter Julian.
"Mr. Carter is voicing an opinion that's other than what the Conservatives want him to voice — so their instinct is to try to attack. And this is what they've done about opponents to Keystone, that are growing in the United States. It does not help the cause.
"If the Conservatives feel strongly about Keystone, what they need to do is put in emissions regulations. They need to put in place clear environmental initiatives around oilsands development."
Also on HuffPost