Why Control of the Senate May Not Be Known Until December

Election Day is November 4, but we may not know until December whether Democrats or Republicans will control the Senate in 2015.

It could all come down to Louisiana, where Sen. Mary Landrieu - the last Democrat holding a statewide office in the increasingly red Creole State - is making a bid for a fourth term, with polls showing her neck-and-neck with her leading Republican challenger, Rep. Bill Cassidy.

Louisiana doesn't have a traditional party primary system; instead, the primary and general election are held on the same day in what is known as a "non-partisan primary," referred to informally as a "jungle primary." All qualified candidates run at once, and if no one candidate wins over 51 percent of the vote on November 4, the election will proceed to a December 6 runoff between the two candidates with the most votes.

So in a year filled with close Senate races, one of the most hotly contested may not be over for an extra month. Analysts have predicted that a Republican takeover of the Senate is within reach, and if control of the upper chamber remains up for grabs on election night, the nation could be left watching and waiting for Louisiana's race to end.

The chances of a runoff between Landrieu and Cassidy are likely increased by the presence of a third candidate on the ballot: tea party favorite and political newcomer Col. Rob Maness. Friday marks the close of the candidate sign-up period in Louisiana, and with Maness expected to qualify as a Republican, the stage is set for a three-way race in November.

Maness is not considered a serious contender by the measures of fundraising and polling, but the presence of a third candidate in the already tight race makes a runoff "pretty certain," according to Pearson Cross, the head of the political science department at the University of Louisiana at Lafayette.

"If Landrieu and Cassidy were mano a mano and someone was going to get 50 percent plus 1, I think you know that would make things a little clearer for both candidates," Cross told ABC News. "With Maness in the race, it makes it hard for one of those candidates to get over 50 percent."

In a midterm season in which Democrats are playing defense in an effort to maintain a narrow majority in the Senate, it's not inconceivable that Louisiana could become the final outpost.

In that unlikely-but-possible scenario, extra attention and money would almost certainly pour into the state.

"Let's imagine it's Wednesday after Election Day and the Senate has 49 Democrats and 50 Republicans elected," said Michael Malbin, the executive director of the Campaign Finance Institute. "In that situation, the runoff election will decide control of the Senate and in that case, everyone will have a stake in the election, because control of the institution will turn on it."

Under that situation, Malbin said the "sky is the limit" when it comes to how much money independent groups might spend on the race.

"It's impossible to predict how much independent spending would occur in that final month," he said. "But you can only expect that anyone with a stake in public policy will spend as much as they can. You can imagine some sort of record would be set."

Louisiana's race may find some clarity soon.

The passing of the qualification period also marks the beginning of the formal campaign season in Louisiana, when average voters begin to tune into the political chatter and do their homework on the candidates.

"After qualifying, [the election] takes on a reality that it didn't before, and you see broader swaths of people paying attention," said Cross.

Though Maness is expected to pull some conservative voters away from Cassidy in the general election, Cross said he may end up actually helping Cassidy more than he hurts him.

"Maness will prevent Cassidy from getting a first round election victory I think, because they do draw from the same pool," Cross said. "But by the same token, I think if Maness were gone, Landrieu would have a better choice in the first round as well."

That's because runoff elections tend to attract fewer, and more politically motivated, voters than general elections. Sean Cain, an assistant professor of political science at Loyola University, says a runoff would likely break in Cassidy's favor.

"That lower turnout is typically the stronger core partisan voters who are willing to turnout in a runoff election," said Cain. "So, if it's a runoff between Cassidy and Landrieu, I think he has the advantage unless something really changes between November and December."

Despite the fact that Maness trails behind his opponents in fundraising and polling, his campaign is pushing the possibility of a scenario - perhaps a far-fetched one -- in which Maness could advance to a runoff with Cassidy.

"If the question is, does Maness think he can get 34 percent of Louisianans to choose the non-politician in this race - absolutely," said Maness campaign communications strategist Kurt Bardella. "Quite frankly, it wouldn't surprise us one bit if come November, both Bill Cassidy and Maness end up advancing to a December run-off and the voters reject Mary Landrieu outright."

But before any scenario of a runoff has the chance of becoming political reality, there are still 10 weeks to go before November election.

Like Maness, both Landrieu and Cassidy are expressing optimism publically, while also acknowledging that it's a tight race ahead.

Landrieu touts her clout in the Senate as one her campaign selling points, while Cassidy counters that her clout hasn't brought real results for Louisiana.

"With my service, Louisiana has real clout and now holds the gavel of the Senate Energy Committee," Landrieu told reporters after qualifying for the ballot Wednesday, according to her campaign. "But this clout isn't mine, it's the people of Louisiana's and with this clout, we will be able to create thousands of high-paying energy jobs in Louisiana and secure America's energy independence."

"You can speak of clout, but frankly you should ask, 'Why haven't you been effective? Why weren't you able to get a vote on Keystone Pipeline,'" The Times-Picayune quoted Cassidy as saying after he qualified for the ballot on Wednesday.

Landrieu has also been weathering a controversy as of late surrounding her use of taxpayer funds to pay for charter flights to two separate campaign events. Though Landrieu has called the incidents a mistake and has taken action to reimburse the flights, it has provided fodder for critics seeking to paint Landrieu as a wealthy politician who's lost touch with her roots.

For Landrieu, one advantage may come on the debate stage.

Landrieu has agreed to four debates and Maness to seven, but Cassidy has yet to commit to any. Cassidy campaign spokesman John Cummins has said that Cassidy will wait until the close of the qualifying period before agreeing to any debates.

Louisiana State University political science professor Robert Hogan said part of Cassidy's calculation in not committing to debates sooner may have to do with the fact that he knows that Landrieu is a "very good" debater.

"A lot of peoples' criticism of [Cassidy] is that he doesn't have the retail politics skill compared to Landrieu," Hogan said. "A high stakes debate ... is an unknown for Cassidy. Landrieu is someone who has devastated her opponents in debates."

Both Landrieu and Maness have criticized Cassidy for not yet committing to any debates. Maness has even taken to tweeting out a photo of a duck wearing a "Congressman Cassidy" name tag with the accompanying hashtag #duckingdebates.