BATON ROUGE, La. (AP) — Republican Bill Cassidy has defeated Democratic Sen. Mary Landrieu, giving the GOP another victory in the final election of the 2014 midterms.

Cassidy's win in Louisiana's Saturday runoff pushes the Republican's new Senate majority to 54 seats in January and costs Democrats their last Senate seat in the Deep South.

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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 GOP gains across Southern states and the strong unpopularity of the president.

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