Republicans seem poised to expand Senate majority with Louisiana race
Louisiana Sen. Mary Landrieu speaks with attendees of the 2011 National Guard Family Program National Volunteer Workshop, July 25, 2011. (U.S. Air Force photo/Sgt. John Orrell)

Republicans appear poised to expand their Senate majority with a runoff election in Louisiana on Saturday that would cap big wins for their party in the Nov. 4 midterm elections.

Republican Representative Bill Cassidy is running against Democratic incumbent Mary Landrieu, the top Democrat on the Senate Energy Committee, and has a comfortable lead in polls.

If he wins, he would be the ninth Republican to capture a previously Democratic seat. His victory would give Republicans 54 seats in the 100-member Senate, enough for a majority but not the 60 seats needed to avoid the tactical blocking procedure known as a filibuster. This means that Republicans, who also control the U.S. House of Representatives, would have to work with Democrats to pass most legislation.

The runoff is being held because no candidate garnered more than 50 percent of the vote on Election Day. A RealClearPolitics average of polls in recent weeks shows Cassidy leading by more than 17 points.

Last month, Landrieu tried to prove her energy industry credentials by pushing a vote in the Senate to force approval of the planned Keystone XL pipeline from Canada's oil sands to the U.S. Gulf Coast. But the vote failed.

Landrieu has turned to sharp personal criticisms of Cassidy.

"I'm running against a guy who is hiding," Landrieu told supporters days before Saturday's vote, castigating Cassidy for not participating in more debates. "And now we know why - because he was double-dipping at the taxypayer expense."

In allegations that surfaced on Louisiana political blogs and that Landrieu has seized on, Cassidy, a doctor, is accused of falsely filling out some timesheets and failing to file others for a part-time Louisiana State University hospital job after he joined Congress in 2009.

Cassidy has denied the allegations of wrongdoing and said they are misguided. His campaign has said they are a desperate attempt to discredit him.

A Louisiana State University spokesman says the school is reviewing the case.

Cassidy supporters have focused on tying Landrieu to President Barack Obama, who is unpopular in the state. One recent 30-second anti-Landrieu video released by Ending Spending Action Fund featured nine separate images of Obama.

Landrieu's struggle mirrors that of two other southern Democratic senators defeated in the midterms: Mark Pryor of Arkansas and Kay Hagan of North Carolina. Like much of the U.S. South, Louisiana has become much more conservative in the 18 years since Landrieu was first elected to the Senate.

(Reporting by Gabriel Debenedetti in Washington and Jonathan Kaminsky in New Orleans; Editing by Frances Kerry)