To build or not to build?

That question is at the heart of the debate over the Keystone XL oil pipeline.

The answer, and the fate of the $8 billion project, depends on what happens in Congress, the courts, the White House and with TransCanada, the company planning to construct it.

The odds of building seem to change almost daily.

A lawsuit is tossed out, then some others filed. The Republican-controlled Congress is poised to approve a bill authorizing construction, despite a White House promise of a veto. The State Department, after stalling its review because of a Nebraska court case, gives federal agencies a new deadline to weigh in.

The 1,179-mile pipeline, first proposed in 2008, would carry an estimated 800,000 barrels of tar sands oil from Canada into the United States, connecting with existing pipelines leading to Gulf Coast refineries.

For environmentalists, approval would prove catastrophic for the global climate and erode efforts by President Barack Obama to rein in heat-trapping emissions.

For Republicans, who have made it their first order of business in the new Congress they control, the pipeline is critical to supplying the country with jobs and with oil from a friendly neighbor, rather than the Middle East.

A look at the major players and where they stand:

CONGRESS

The House this month passed legislation approving, for the 10th time, the pipeline’s construction. Identical legislation cleared an initial hurdle in the Senate, where a 63-32 vote was three more than the 60 required, but not enough to override a veto.

The Senate is now considering dozens of amendments. On Wednesday, it overwhelmingly adopted, 98-1, a measure saying climate change is not a hoax and real, but Republicans refused to back two others that said human beings contributed to the problem. The scientific consensus is that burning fossil fuels is behind climate change.

Republicans intend to offer other additions, including one that would say the Senate rejects international agreements to reduce heat-trapping pollution that would harm the U.S. economy.

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THE WHITE HOUSE

The White House explained the veto threat by saying it had to wait for the outcome of a Nebraska court case and the State Department review to play out.

Obama’s remarks about the pipeline have gotten increasingly negative in recent months, emboldening environmental groups who have called on him to reject the pipeline outright. In his State of the Union address Tuesday night, Obama urged Congress to “set our sights higher than a single oil pipeline.”

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THE COURTS

Opponents in Nebraska reignited the legal fight last week, filing two new suits over its proposed route.

They came from seven landowners in Holt and York counties who have received written warnings that TransCanada plans to file eminent domain papers to gain access to their land.

The landowners’ lawyer, Dave Domina, said TransCanada’s written warnings give the plaintiffs a clear legal basis to challenge the project. That’s a key issue, because the Nebraska Supreme Court tossed an earlier, similar suit, with three judges saying those plaintiffs failed to meet the threshold. The judges’ decision removed an obstacle to the project and was a major reason the White House’s threatened a veto.

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THE STATE DEPARTMENT

The department has given federal agencies until Feb. 2 to weigh in on whether the pipeline serves the national interest, a determination required for all border-crossing pipelines. That gives agencies specializing in the environment, commerce and other matters just weeks to file their opinions.

The department didn’t set a timeline for when it would make its long-awaited judgment on whether the pipeline was in the U.S. national interest.

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THE COMPANY

With the state court removing a legal barrier, TransCanada has filed paperwork in nine counties to acquire access to the remaining land that’s needed to construct, operate and maintain the pipeline.

By law, TransCanada can use the courts to force landowners to sell access to their land. Company officials say they still need to acquire 12 percent of the total land easements from landowners who have not yet reached a deal. Some holdouts have said they won’t negotiate.

The route still faces legal challenges in Nebraska, where two new suits have been filed.

(AP)