BATON ROUGE, Louisiana — Republicans increased their new majority in the Senate to 54 seats as the final election of the nation’s 2014 midterms ended with a defeat for Democratic Sen. Mary Landrieu.

Republican Bill Cassidy’s win in Louisiana’s runoff Dec. 6 also costs Democrats their last Senate seat in the Deep South.

Landrieu fought to make the election a referendum on her own performance rather than on President Barack Obama. But she was unable to win a fourth term against the wave of Republican gains across Southern states and the strong unpopularity of the president.

Republicans have picked up nine Senate seats in the midterm elections for the 100-member chamber in January.

Cassidy portrayed his candidacy as a way for voters to cast another ballot against Obama’s policies. That mirrored the winning campaign argument of Republicans who ousted Democratic incumbent senators in Arkansas and North Carolina.

Landrieu, 59, whose family has been a New Orleans political dynasty, was criticized for her votes for Obama’s signature health care overhaul and other policies supported by the president. Cassidy repeatedly said the Democratic incumbent voted with Obama “97 percent of the time.”

Cassidy, 57, a doctor, spent little time on the campaign trail in the runoff, as his campaign sought to keep him from making any missteps, while Landrieu crisscrossed the state in appearances as she tried to hang onto her job.

But Landrieu’s campaign was undermined by national Democrats’ near total abandonment of the Senator. Of every dollar spent by outside groups since Louisiana’s Senate race headed into its final month, 97 cents were paid to help Cassidy. Landrieu was largely left to fend for herself.

Her party’s lackluster performance nationally on Nov. 4 undermined the central theme of Landrieu’s campaign, that her clout was invaluable to Louisiana. With Republicans gaining control of the Senate in the new year, Landrieu will lose her Energy Committee chairmanship.

A last-ditch attempt to show that she could break through Congressional gridlock and pass the long-delayed Keystone XL pipeline from Canada to the Gulf Coast fell one vote short of the support she needed from her own party to pass.

(MELINDA DESLATTE)