Mary Landrieu probably wouldn't have won her run-off election in Louisiana even if the Senate had passed her last-ditch bid to approve construction of the Keystone XL oil pipeline on Tuesday evening. But the measure's defeat by just one Democratic vote likely marks a sad final chapter to her three-term tenure.

Having secured 59 votes, including all 45 Republicans, Landrieu needed just one more Democrat to meet the filibuster-proof threshold of 60. She couldn't find that last vote, however, and perhaps it was because the stakes just weren't high enough. While Landrieu and her newfound Republican allies pitched the bill as an opportunity to heed the voters' call for comity and deliver a quick bipartisan win following the midterm elections, Democrats knew that the passage of the Keystone was just a matter of time: They could hold their nose and vote for it now, or they could stick to their opposition on environmental grounds and wait for the new Republican majority to drop it on President Obama's desk in January. On the Senate floor Tuesday, Democrat after Democrat stood up to decry the Keystone project as counterproductive to the U.S.'s efforts to reduce its carbon footprint and its dependence on fossil fuels for energy.

The only person who really needed the Keystone victory in November was Landrieu, who is trying to hold off Representative Bill Cassidy in Louisiana's run-off election on December 6. Democrats allowed Landrieu her vote on the bill, but the cold calculation that most of them made is that with the limited polling out of Louisiana showing her losing by double digits, passage of the bill—which also had Cassidy's name on it—wouldn't be enough to save her.