NEW ORLEANS -- Louisiana's fiercely fought Senate race is headed to a runoff that will decide the size of the GOP's Senate caucus, after neither incumbent Democrat Mary Landrieu nor Republican challenger Rep. Bill Cassidy won a majority on Election Day.
Early results showed that tea party Republican candidate Rob Maness seemed to have shaved off enough votes from Landrieu and Cassidy to force the race into a runoff. Under the state's unusual "jungle primary" system, Landrieu will now face Cassidy again in a December rematch.
Polls suggest that Cassidy will have the edge in the runoff: A HuffPost Pollster average of a head-to-head matchup shows him leading Landrieu 49 percent to 44 percent.
But the GOP seizure of the Senate takes some pressure off Landrieu, who now has a chance to make the runoff election center on local issues.
"This race is not about who the president is, who the president was, or who the president will be, or which party controls Congress," Landrieu said in a speech after the runoff was called. "This race is about the future of Louisiana."
Cassidy, on the other hand, argued that the runoff would be a referendum on Obama's presidency
"It's going to come down to one fundamental issue: Do you want a senator who represents Barack Obama, or a senator who represents you?" Cassidy shot back.
Democrats and Republicans had expected the runoff, which will extend the grueling and expensive political dogfight. Both sides have already reserved a reported $10 million worth of television and radio ads in Louisiana for the added month of campaigning, according to The New York Times.
"This is not over yet. If you have stock in a TV station, you're join got make a lot of money," joked Cassidy on Tuesday night.
The Louisiana runoff means that the total number of Senate seats picked up by Republicans this cycle will remain unclear for at least several more weeks.
Throughout the race, Landrieu struggled to distance herself from President Barack Obama, who is deeply unpopular in the state. Last week, she suggested that southern voters dislike Obama in part because of his race, a move observers said may have been designed to increase African-American turnout.
Cassidy, a doctor who was first elected to the House of Representatives in 2008, has made his name in part by criticizing the Affordable Care Act. But his support on the right was undermined by the perception that he was too soft on issues like immigration, and by the revelation that he donated to Landrieu in 2002. Cassidy will need to convince supporters of Maness -- a right-wing candidate who was endorsed by figures like Sarah Palin and Glenn Beck -- to return to the polls and vote for him this time.
While Maness did not immediately endorse a candidate in his concession speech, he has said he will support whoever is the GOP candidate on December 6.
Landrieu will be counting on women and blacks to turn out big in December, and will need to keep the race from becoming another referendum on Obama. She is an experienced campaigner who has pulled out several tough Senate victories before, including her first race in 1996, which she won by just 6,000 votes.
"I don't like to say never. I've written her off before and she continues to find a way to pull that rabbit out of a hat," Bob Mann, a journalism professor at Louisiana State University, told The Huffington Post on Monday.
Mann said Landrieu is struggling against demographic headwinds in a state where white voters have shifted dramatically against Democrats in the last 30 years. But a Republican takeover of the Senate helps Landrieu in the runoff.
"Louisiana conservatives may feel that the message has been sent to Obama loud and clear," he said. "Some of that anger may dissipate just enough to help her."
This story has been updated.