WASHINGTON, D.C. - The Senate on Tuesday narrowly rejected a bill to fast track construction of the Keystone XL pipeline as an insufficient number of Democrats joined with their Republican colleagues to overcome the 60-vote threshold necessary for passage.

The bill failed by one vote, with a final tally of 59 to 41.

The loss could be a blow for Sen. Mary Landrieu, a Louisiana Democrat and cosponsor who pushed the Democratic leadership to put the bill up for a vote in recent days. Their decision to do so was largely seen as a move to help her win re-election to her Senate seat in a Dec. 6 runoff. Polls show her trailing.

In the hours before the vote, Republicans indicated that they wanted to put the onus on President Obama to make a final decision. Had the bill passed, the House version with identical language would have gone to his desk for a signature.

Sen. Pat Roberts, R-Kansas, said the president, "owes the American people an answer as to whether he supports this project or not."

But the delay is likely to only postpone the inevitable for Mr. Obama. In January, Republicans will take over the Senate with at least a 53-seat majority. That figure will rise to 54 if Landrieu loses to Rep. Bill Cassidy, R-Louisiana, who authored the House's Keystone XL bill that passed last week.

The bill's failure came down to insufficient Democratic support. Several lawmakers in the hours beforehand expressed their opposition on the Senate floor.

"It's just plain dangerous because it will transport the dirtiest oil on the planet. Forcing the approval of the Keystone [pipeline] when so many concerns remain does not allow for the kind of review that our affected communities deserve," said Sen. Barbara Boxer, D-California, Tuesday. "To stand here and say this is the absolute job producer is phony. It is phony baloney."

She warned that, "To go blindly down this path is a huge mistake."

Sen. Barbara Feinstein, D-California, said, "On the economics of the pipeline, there is simply not enough benefit to outweigh the environmental damage."

Some Democrats who have indicated they are "yes" votes found themselves the subject of protests by climate groups Tuesday afternoon. They carried banners to the offices of Sens. Tom Carper, D-Delaware, and Michael Bennet, D-Colorado, and accused the two senators of voting like climate change deniers.

The proposal passed by the House Friday says that TransCanada can construct and operate the pipeline. Crude oil harvested from Canadian tar sands would be carried by the pipeline to oil refineries along the U.S. Gulf Coast.

The project has been delayed for several years by the State Department's environmental review process. Its analysis, released in January, found the project would pose no "significant" environmental danger. In April, however, Mr. Obama's administration indefinitely extended the amount of time agencies have to review the project, citing continued legal wrangling over the pipeline's route through Nebraska.

If signed into law, the bill passed by the House would have effectively ended the debate over the project's environmental impact. It would recognize the State Department's analysis as the final verdict on the matter and clear the way for construction to begin.

US Senator Jim Inhofe, R-Oklahoma, senior member of the Environment and Public Works Committee, released the following statement after the US Senate's failure to pass the bill to approve to the Keystone XL Pipeline:

"Despite the US Senate failing to approve the Keystone XL Pipeline, I am proud to have voted in favor of the legislation and to have stood once again in defense of thousands of well-paying American jobs and a more robust energy sector. The Keystone pipeline was in need of approval years ago, and I fully expect that the Keystone legislation will see the light of day in a new Congress. The US energy sector has provided over 9.2 million jobs to Americans, and I will continue to work alongside my colleagues who championed a thriving US economy today. The Senators who voted against the Keystone XL Pipeline had an opportunity to stand for job creation, energy independence, and national security, but failed to lead the way."