The tortuous six-year fight over a controversial proposal to funnel oil from Canada to the Gulf Coast took another turn this week after both houses of the lame-duck Congress moved to vote on the Keystone XL pipeline.
As the legislation barrels through Congress and heads to the Oval Office, President Barack Obama may soon settle one of the most politically charged debates of the decade. The White House appeared to downplay the congressional maneuvering Wednesday, saying it takes a "dim view of these kinds of legislative proposals."
But if the Senate passes the bill as early as next Tuesday, Obama would likely be forced to either sign it into law or veto it. He has said the project needs his approval because it crosses an international border.
Here's a look at what the Keystone XL pipeline would mean for the country and why it's been one of the most contentious issues of the Obama era:
What is Keystone XL, anyway?
It's a pipeline system that would double the flow of heavy tar sands oil from Canada down to refineries in the Gulf Coast. For the last six years, the Obama administration has been weighing whether to sign off on the northern part of the project, which would transport roughly 830,000 barrels of oil per day from Alberta, Canada, to Steele City, Nebraska, and then to Texas.
The Keystone XL is being constructed by a Canadian energy company, Trans Canada. The northern leg of the system is projected to cost an estimated $5.4 billion. Other legs of Keystone have been around since 2010, carrying tar sands oil from Hardisty, Alberta, to refineries in the American Midwest and the Gulf Coast.
Who wants to build it?
Republicans, several moderate Democrats, labor unions, oil companies and the Canadian government want Keystone XL approved.
What's their argument?
In more than half-a-decade of debate, proponents have argued that the construction of the northern leg would create tens of thousands of jobs that could supercharge limp economies in the heartland.
A massive State Department report earlier this year found that building the pipeline would support roughly 42,100 jobs over a two-year construction period — and contribute approximately $3.4 billion to the economy, or about 0.02 percent of GDP.
Who wants to scrap it?
Environmental groups, green activists, and many liberal Democrats have lobbied hard against the pipeline.
What's their argument?
The pipeline's opponents have argued the project would speed up climate change, saying the production process would lead to more carbon dioxide emissions. The State Department found that oil from Alberta's tar sands produces 17 percent more greenhouse-gas emissions over its life-cycle than regular oil — something many environmental groups say would exacerbate global warming.
Many activists have claimed building the pipeline risks global catastrophe. James Hansen, the former NASA climate scientist, has said tapping the tar sands of Alberta would mean "it's game over for the planet."
Why it is coming to a vote now?
The answer has a lot to do with the still-undecided Louisiana Senate race, actually.
In a stunning move Wednesday, Senate Democrats abandoned long-running efforts to block the measure in the hopes of helping Sen. Mary Landrieu win a December runoff and hold onto her seat in energy-rich Louisiana. Republicans hit back by scheduling a vote in the House on Thursday on a similar bill sponsored by Rep. Bill Cassidy, Landrieu's GOP opponent in the Dec. 6 contest.
In recent years, the GOP-controlled House voted several times to back the pipeline, while the Democrat-led Senate — taking cues from the White House — has held off on holding a vote.
What happens if it passes?
White House spokesman Josh Earnest said Wednesday that the Obama administration has taken a "dim view of these kinds of legislative proposals in the past" and suggested that Obama may veto the measure if it arrives at his desk.
"Evaluating those earlier proposals, we have indicated that the president's senior advisers at the White House have recommended that he veto legislation like that," Earnest told reporters today in Myanmar, where Obama is attending a summit. "And that has continued to be our position."
A veto from Obama could challenge Congress to override him.
The Associated Press and Reuters contributed to this report.