Keystone has created a political headache for the president, and any decision from the oval office is sure to infuriate a key Democratic constituency. Labor unions have pressed Obama to approve the oil-sands pipeline, which would send heavy crude from Canada to the Gulf Coast, while environmentalists have loudly called for its rejection, saying that approval would worsen global warming.
Looking past Obama's looming veto threat, the president may reject Keystone as part of a broader calculation aimed at shoring up his environmental legacy.
And if the president opts to reject, he will have no shortage of excuses to say "no."
Obama has said that he will not approve the project if it significantly adds to the problem of climate change.
The State Department concluded in its analysis of the pipeline that Keystone XL would have minimal environmental impact. But falling oil prices could change that calculation. Earlier this month, the Environmental Protection Agency warned that low prices could intensify the pipeline's environmental impact.
In recent months, the president has also voiced concerns about the project's potential to worsen global warming.
"I want to make sure that if, in fact, this project goes forward, that it's not adding to the problem of climate change, which I think is very serious and does impose serious costs on the American people," the president said during an end-of-the-year press conference in December.
Obama downplayed the pipeline's potential to create jobs, at the same press conference.
"Now, the construction of the pipeline itself will probably create a couple thousand jobs. "¦ But when you consider what we could be doing if we were rebuilding our roads and bridges around the country ... we could probably create hundreds of thousands of jobs, or a million jobs. So if that's the argument, there are a lot more direct ways to create well-paying American construction jobs," Obama said.
Regardless of how Obama weighs in, Republicans have vowed to keep pressing for the project's approval.
Sen. John Hoeven of North Dakota, a sponsor of the legislation that passed in the House on Wednesday, has pledged to attach pro-KXL legislation to future energy bills as well as must-pass spending bills that the president would be hard-pressed to veto.
And while Obama and Republicans clash symbolically over Keystone, project developer TransCanada is making fresh attempts to convince the State Department that it should green-light the pipeline.
On Wednesday, the company pushed back against EPA's recent claim that the collapse in oil prices should prompt State to revisit its conclusion that building Keystone would not cause a substantial increase in greenhouse gas emissions.
"TransCanada rejects the EPA inference that at lower oil prices the project will increase the rate of oil-sands production growth and accompanying greenhouse-gas emissions. These conclusions are not supported by the facts outlined in the Final [Supplemental Environmental Impact Statement] or actual observations of the marketplace since TransCanada submitted its first application for the Project in 2008," CEO Russ Girling said in a new letter to the State Department.
Ben Geman contributed to this article