Another issue that took center stage during the final month of the extended campaign was the candidates' support for construction of the Keystone XL pipeline.
Both Cassidy and Landrieu tried to lay claim to the oil transportation system, with the two politicians angling to slap their names on legislation to approve it.
As soon as the Senate returned from a six-week recess after the midterm elections, Landrieu, the chair of the Senate's Energy and Natural Resources Committee, tried to rally Democrats to send a bill to the president giving the pipeline's maker, TransCanada, permission to begin construction on the proposed route.
Conservative estimates say that construction of Keystone XL will create 3,900 jobs and another 38,000 jobs indirectly, many of which could end up benefiting oil-rich Louisiana. More aggressive counts push the total number of jobs on the line up to 119,000.
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Bill Cassidy
The Obama administration put a federal permit on hold indefinitely last spring for the XL section of the pipeline amid strong-arming from environmental groups. It has since said it would wait for a Nebraska court to make a ruling on the proposed pathway for the pipeline before it reconsidered its position.
The decision from the Nebraska Supreme Court will be announced any day now.
During Landrieu's Hail Mary negotiating in the Senate the White House said it took a 'dim view' of her legislative strategy to ram though a bill at the end of the year to approve the pipeline, but it would not say whether Obama would veto her bill if Congress sent it to the president's desk.
In the end, he didn't have to. The GOP-controlled House voted to advance the Senate's bill, but Landrieu fell one vote short of being able to overcome a filibuster in the upper chamber from her own party.
While all 45 Republicans in the Senate voted for the bill, only 13 of Landrieu's of allies did the same.
Landrieu has made her leadership post in the Senate a key focus on her campaign, arguing that if reelected, she'll push back against government regulations that would hamper her state's energy-heavy economy.
The Keystone vote was her last opportunity to convince voters that when push comes to shove, she could deliver on behalf of her state.
In another blow to Landrieu, however, incoming Senate Majority Leader Mitch McConnell offered Cassidy a seat on the Energy Committee if he were to win today's race, putting him on roughly the same playing level with his incumbent opponent.
Even if she had been reelected, Landrieu would have no longer been in charge of the Energy committee due to the forthcoming reconfiguration of the Senate caused by Republican wins in last month's off-year elections.
Seeing the writing on the wall, Landrieu hit out on Wednesday at the Democratic Senatorial Campaign Committee for not directing more resources her way.
'I am extremely disappointed,' she said. 'You know, they just walked away from this race.'
The Center for Public Integrity had revealed earlier that day that groups aligned with Landrieu had run fewer than 100 ads since Nov. 5.
Cassidy backers, on the other hand, bombarded the airwaves with 6,000 commercials throughout the last month.
And while Landrieu had purchased 3,000 spots of her own, Cassidy single-handedly beat her out in that arena as well, blasting 5,000 ads in less than 30 days.
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