Can a group of U.S. senators really bypass the Obama administration and force approval of the controversial and long-delayed Keystone XL pipeline?

“The review process has been thorough,” said Senator Mary Landrieu (D-La.), who introduced a bill to approve the pipeline with Senator John Hoeven (R-ND) last week. “The five studies that have been conducted, as required by law, are complete. It is time to stop studying and start building.”

The pipeline, which would carry crude oil from Canada to refineries on the U.S. Gulf Coast, has been under review for more than five years.

In April, the State Department extended the review process indefinitely, citing pending litigation in Nebraska and the need to study the “unprecedented” number of public comments it had received.

“The legislation Senator Hoeven and I have introduced will green-light the construction of the pipeline immediately,” Landrieu said in a statement.

The idea of pushing past the White House to expedite Keystone XL is certainly appealing to proponents of the pipeline. But after years of controversy, is it just more political posturing or could it really work?

The answer seems to be that there’s a reasonable legal case for overriding the president on the issue, but the necessary votes probably aren’t there.

Measuring Impacts

The history of the project is politically fraught.

The State Department, charged with reviewing Keystone XL because it crosses international boundaries, rejected the project in 2011, in part because of concerns over its route through Nebraska’s Sandhills region, a native grasslands that contains one of the largest aquifers in North America.

TransCanada, the pipeline’s Calgary-based operator, revised the Nebraska route and resubmitted the application for the presidential permit two years ago.

The new route addressed some of the environmental concerns about Keystone, but not about the pipeline’s broader impact on emissions and climate change. President Obama has said that he would approve the pipeline only if it “does not significantly exacerbate the problem of carbon pollution.”

In January this year, the State Department’s final environmental impact statement seemed to address that concern, saying the pipeline was “unlikely to significantly impact the rate of extraction in the oil sands or the continued demand for heavy crude oil at refineries in the United States.”

That is because oil transport by rail has surged, filling the gap in pipeline capacity—and raising safety and environmental questions similar to those surrounding the pipeline.

The Legal Debate

Senator Hoeven has been trying unsuccessfully for the past two years to move Keystone XL forward with congressional action. He points to research he requested in 2012 that says the commerce clause of the Constitution gives Congress the authority to approve such projects.

The report from the Congressional Research Service said that legislation to approve the Keystone project “appears likely to be a legitimate exercise of Congress’s constitutional authority to regulate foreign commerce.”

The same report also noted that the executive branch’s ability to act on cross-border project permits was covered under its own constitutional power to conduct foreign affairs. And there isn’t much precedent for congressional challenges to executive authority in this area, the report said.

Still, if Keystone proponents in Congress could muster the political force to pass legislation, it seems they would be on firm legal ground.

“Although I hope that Congress doesn’t intervene, I think it’s pretty clear that they have the power to do that, since the Constitution explicitly gives them the power to ‘regulate commerce with foreign nations,’” Daniel A. Farber, a law professor and co-director of the Center for Law, Energy, and the Environment at the University of California, Berkeley, said via e-mail.

There could still be a court challenge, of course. “There’s no way of knowing, but just about anything the government does these days prompts a lawsuit, so I wouldn’t be surprised,” said Farber.

The Political Debate

Landrieu and Hoeven represent states that stand to benefit economically from the TransCanada pipeline: Louisiana’s refineries are hungry for discounted Canadian heavy crude to replace declining production from Mexico and South America; North Dakota is seeking outlets for its own ever-increasing production of oil from the Bakken shale. (A little more than 10 percent of the pipeline’s 830,000 barrels per day capacity would be set aside for Bakken crude.)

Hoeven suggests that the State Department has already done the work necessary to determine whether Keystone XL should go forward. “The Keystone XL pipeline project has been under review for more than five years, with four favorable environmental reports completed to date,” he said in a statement.

David Goldston, director of government affairs for the Natural Resources Defense Council, disagrees. He warns against the idea of legislators taking on work that, in his view, should be done by the federal agencies that are accustomed to evaluating such projects.

“I doubt that most folks on [on Capitol Hill] have read through [the State Department analysis] in its entirety,” Goldston says. “Agencies are still in the process of weighing in on it … Congress acting as a permitting agency doesn’t seem like a very wise policy approach.”

“A Real Challenge”

The push to hold a vote on Keystone XL comes as the Senate weighs a different bipartisan energy bill on Tuesday: the long-delayed Shaheen-Portman measure on energy efficiency. That legislation would strengthen efficiency standards for federal, commercial, and residential buildings and boost investment in energy-saving technologies, among other things.

Keystone proponents may use the Shaheen-Portman bill as leverage to get progress on their issue. Senate Majority Leader Harry Reid has said he is “open to anything” that will move Shaheen-Portman forward, but has not yet signaled whether he will allow a binding vote on Keystone.

Last year, the Senate passed a nonbinding resolution in favor of building Keystone XL with 62 votes.

But even if the Senate passed a binding bill, then won easy approval in the House and was able to send legislation to President Obama, it would need 67 votes to override a presidential veto. Hoeven said last week on C-SPAN that getting even 60 votes would be “a real challenge.”

The American Council for an Energy-Efficient Economy, which has been pushing the Shaheen-Portman bill, wrote in a blog post Monday that amid the battles over Keystone, health care, natural gas exports, and other issues, “It’s easy to forget that there is an energy-efficiency bill in there that does not get much press attention … Why? Because nobody is fighting over it!”