new orleans—In places where there is a contested Senate race, chances are it is the most expensive midterm election in state history. Louisiana is no exception. Federal Election Commission filings show well over $30 million spent by candidates and outside groups.

At a raucous gathering for Senator Mary Landrieu on Saturday, Hillary Clinton reminded the crowd of this fact in particularly charged language for New Orleans, where the rally was being held. “There has been a flood of outside money trying to muddy the waters, drown your voice, discourage people from voting,” she said.

If the Senate election here heads to a runoff, there might be actual dump trucks of money coming across the state line, particularly if the seat will end up determining control of the upper chamber. Taking a closer look at who is spending the money—and who isn’t—is an easy way to pick up on some of this race’s unique contours.

Louisiana is one of only two contested Senate races where the US Chamber of Commerce isn’t involved. (The other is Arkansas.) As we noted last week, the Chamber has an enormous footprint wherever it goes, averaging close to $1 million per race. It’s the biggest spender in twenty-eight of the thirty-five contests it is involved with this cycle.

But it hasn’t spent a dime attacking Landrieu nor boosting her opponent, Republican Representative Bill Cassidy. This likely reflects a desire not to make an enemy of Landrieu were she to hold onto the seat, since she is the chair of the hugely powerful Senate Energy and Natural Resources Committee.

It’s a huge boon to Landrieu not to have a heavyweight like the Chamber pummeling her in the state, and it’s one of many ways her chairmanship has become a key asset in the campaign. Speaker after speaker at Saturday’s rally reminded potential voters how important Landrieu’s position is for the state, where over 400,000 jobs rely on the oil and gas industry.

“Nobody can tell the people of Louisiana that ‘Hey folks, we’re gonna vote to replace the chairman of the United States Senate Energy Committee, the most important committee…to the state of Louisiana, with a new first-term senator,’&thin;” said former Senator John Breaux. “We’re not gonna buy that. That would be like saying we’re going to kick Drew Brees out of being quarterback and replace him with a freshman quarterback from some high school.”

Though the Chamber isn’t actively backing Landrieu, many oil and gas companies are. Exxon Mobil, NRG Energy and Dominion Resources are three of the top five contributors to her campaign committee. They don’t even appear in Cassidy’s top twenty.

Landrieu is benefiting greatly from the oil companies’ support, and the non-support of the Chamber. The industry surely expects the favor to be returned if she holds on, which would have long-ranging impacts for the state and national energy policy going forward. (Zoë Carpenter explored this at length in our October 1 issue.)

But not every oil and gas producer has made the same calculation. The Louisiana Oil & Gas Association is supporting Cassidy, citing a bigger picture. “It’s not about the job that Mary has done, it’s about who controls that Senate,” the group’s president, Don Briggs, told Politico.

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The changing politics over gun control are also visible in the FEC filings for this race. Landrieu voted for the universal background check bill that was pushed in the wake of the Newtown shootings last year—something many observers saw as a courageous vote for such a rural, gun-loving state.

Accordingly, the National Rifle Association has dropped almost $2.3 million to defeat Landrieu this cycle. The NRA is the fifth-biggest-spending outside group involved on either side of the race, with $1.7 million, and the NRA Institute for Legislative action is seventh with $529,000.

But sandwiched in between, as the sixth-biggest-spending group, is Americans for Responsible Solutions, the pro-gun reform group founded by Gabby Giffords and her husband Mark. It has spent $570,000 on the race so far, which doesn’t cancel out the NRA, but surely helps blunt its impact.

One needs only to look north to Arkansas to see why Landrieu’s support for background checks was a smart play in terms of campaign finance. (To say nothing of the moral and policy imperatives.) There, Democrat Mark Pryor is also locked in a tough battle. He voted against the gun bill—and the NRA is backing his Republican opponent anyway. And Pryor has none of the money from the Giffords group.

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There is a unique ideological split among conservatives in this race—Tea Party favorite Rob Maness is pulling around 9 percent of the vote in most polls. The GOP base was already skeptical of Cassidy’s ideological purity, and Maness, a former Army colonel, has been boosted by endorsements from conservative icons like Tony Perkins and Sarah Palin.

Maness is unlikely to win (Palin’s prognostications aside) but he could easily force this race into a runoff by denying Cassidy more than 50 percent of the vote. To that end, Cassidy held a rally in St. Tammany Parish on Saturday with Dr. Ben Carson, a conservative icon in his own right who makes headlines by frequently comparing Obamacare to slavery.

Though he might have low poll numbers, Maness is doing better in the outside-spending race. The Senate Conservatives fund has dropped $442,430 into the race to support him, making it the ninth-highest-spending outside group. This is helping Maness with valuable exposure to state conservatives, and if Louisiana’s Senate race does indeed end up in a runoff, that half-million dollars could be a big reason why.