— The U.S. Senate race in Louisiana ranks with the most-watched elections in the country this year, a pivotal contest in the Republicans’ drive to capture a Senate majority. So when the next deadline arrives on Oct. 15 for candidates to file their campaign finance reports, there is sure to be a flurry of media reports and blog posts about who has raised how much, who has spent what and who has the most on hand to make it through the rest of the campaign.

Will Mary Landrieu, a vulnerable Democrat in a red state, take in more money than her Republican challengers and win re-election with a majority of the vote in the open primary Nov. 4?

Will Republican U.S. Rep. Bill Cassidy, of Baton Rouge, keep the fundraising pressure on Landrieu and force a Dec. 6 runoff under a scenario favorable to him?

Will tea party Republican Rob Maness, a political newcomer, attract enough contributions to rise from Nov. 4 spoiler to Dec. 6 contender?

What comes out on Oct. 15 will tell only part of the money narrative. The rest of the story — a part that’s less visible and more open-ended — keeps growing, and it plays an ever-increasing role in American politics, in Louisiana and beyond.

The attention-getting Oct. 15 reports, actually, required by law and filed with the Federal Election Commission, will disclose the money raised and spent through Sept. 30 by the official campaign committees controlled by the candidates. That’s a significant part of the money picture, totaling tens of millions of dollars among all three candidates.

Missing from those reports will be millions more — the “outside spending” from an array of groups and organizations that operate under different rules for how much they can accept, whom they can take it from, how much they have to disclose and what they can say in the television advertising that accounts for the bulk of their activity in the election.

The commercial that accused Cassidy of voting to reduce veterans’ benefits? Outside spending.

The one that says Landrieu wants to take away gun rights? Outside spending

And in both cases, the ads were denounced by independent fact-checkers as false or misleading (although many ads paid for by outside groups don’t run afoul of the fact-checkers).

So far, outside spending to boost Landrieu exceeds the amounts aiding Cassidy (and, at a much lower level, Maness). That may reflect Democratic thinking that Landrieu’s best shot is to score a win on Nov. 4 without a runoff, in contrast to Cassidy’s apparent strategy to force a head-to-head matchup with Landrieu on Dec. 6, when the broader national picture of partisan control of the Senate is more vivid. In any case, outside spending is sure to increase in the next month, and it’s likely to escalate dramatically in the event of a runoff.

In 2010, outside spending on all federal elections nationwide (excluding political-party committees) totaled more than $300 million, according to OpenSecrets.org, a website operated by the Center for Responsive Politics that tracks political financing. In the presidential election year of 2012, the total more than tripled, to more than $1 billion. Spending to date indicates the old records — at least for U.S. Senate and House races — will be obliterated in the elections now underway, the site says.

Through Aug. 2, Landrieu’s official campaign reported raising $14 million for her re-election and spending $8.5 million, according to her most recent FEC filing. For Cassidy, the figures were $8 million raised and $3 million spent, and for Maness, $1.5 million raised and $1.3 million spent. That money goes for political advertising, campaign staff salaries, yard signs and other expenses.

Outside spending isn’t reported under the same rules as official campaign financing, and an apples-to-apples comparison isn’t available. But among the well-documented outside groups most active in the Louisiana Senate race through Oct. 1, the Senate Majority Political Action Committee had spent $2.4 million, Patriot Majority USA $2 million and the Democratic Senatorial Campaign Committee $2 million, according to a compilation of FEC filings by OpenSecrets.org. All of that money was spent in opposition to Cassidy (and thus, effectively, on behalf of Landrieu) and virtually all of it on political advertising.

Major spending against Landrieu or in support of Cassidy included $670,000 by the National Rifle Association PAC, $440,000 by the NRA Institute for Legislative Action, $220,000 by the National Draft Ben Carson for President Committee, $115,000 by the Women Speak Out PAC and $109,000 by the Citizens for Conservative Leadership. The Senate Conservatives Fund has spent $319,000 in support of Maness.

Those outlays represent what the FEC calls independent expenditures, which are only one part of the outside-spending universe. Independent expenditures directly aim to promote victory or defeat for a candidate for federal office but, by federal election rules, they cannot be conducted in coordination with the candidate’s official campaign.

Under the rules governing official campaign accounts, candidates can accept no more than $2,600 per election from an individual or $5,000 from a PAC — and they can’t accept anything from corporations or labor unions. But contributions to organizations for independent expenditures aren’t restricted as to amount or source. That’s the result of federal court rulings in 2010 — most famously in the Citizens United case before the U.S. Supreme Court — that struck down such restrictions as an infringement of the right to free speech guaranteed in the First Amendment to the U.S. Constitution.

Until then — beginning with post-Watergate reforms that included creation of the FEC in the 1970s, and continuing through the McCain-Feingold Act of 2002 — the trend in federal law ran toward increasing regulation of money in politics. But those 2010 rulings, in both the Citizens United and SpeechNow cases, reversed that course and opened the floodgates for money to flow to political groups spending on campaigns.

“We think that’s a pretty good deal,” said David Keating, president of the nonprofit Center for Competitive Politics in northern Virginia and a plaintiff on the winning side of the SpeechNow case. “More spending means more information, and more voters turning out.

“The rise in spending is because the courts have recognized that the First Amendment means something when it says, ‘Congress shall make no law … abridging the freedom of speech,’ ” Keating said.

Fred Wertheimer, president of the Washington nonprofit Democracy 21, said the court rulings have set the stage for a return to the corrupt days before the Watergate-era reforms.

“They are doing enormous damage to our political system and our democracy,” he said. “The Supreme Court has opened the door to a relatively few of the wealthiest individuals in the country, corporations and other special-interest groups to buy influence over government decisions and exercise extraordinary and undue influence over our elections.”

Senate Democrats, including Landrieu, voted last month for a constitutional amendment to overturn the Citizens United decision, but it was blocked by Republicans. Landrieu also has publicly deplored the advent of unlimited and undisclosed corporate contributions in the aftermath of the case.

Those 2010 rulings dramatically altered the political-financing landscape, and the dust has not settled yet, as operatives seek new ways to raise and spend money on politics. Currently, most independent expenditures come from three types of organizations:

  • Political action committees (PACs): These have been around for decades and still operate under considerable regulation. They typically are affiliated with a corporation, labor union, trade association or nonprofit organization. PACs can contribute up to $5,000 per year to official campaigns: The Senate Conservatives Fund, for example, is a PAC that has donated $5,000 to Maness. Money collected for campaign donations can come only from individuals and only up to a maximum of $5,000 per person per year. PACs must file regular reports with the FEC disclosing contributors and expenditures.
  • Super PACs: Created in response to the 2010 court decisions, super PACs focus on independent expenditures and may accept unlimited donations from any source for them. Both contributors and expenditures must be reported to the FEC. The Senate Majority and Women Speak Out groups are both super PACs.
  • “Dark money” organizations: These include “social welfare,” labor union and trade association groups that are set up as tax-exempt entities under sections 501(c)4, (c)5 and (c)6 of the federal revenue code. They, too, may accept unlimited donations from any source for their independent expenditures, and that spending must be reported to the FEC. But so long as the main function of the organization is not political — a somewhat squishy criterion — donors need not be disclosed, hence the term “dark money.” And the groups can make unlimited contributions of their own to super PACs, meaning the ultimate source of those contributions remains hidden. Patriot Majority and the NRA Institute for Legislative Action are dark-money groups.

The Center for Responsive Politics does not take a position on whether to limit contributions or spending, but it is concerned about disclosure.

“With the growth in dark-money spending, it’s more important than ever for some kind of transparency to be brought to the system so that voters know who is funding the ads that they’re getting barraged with in their living rooms,” spokeswoman Viveca Novack said.

There’s yet another category of outside spending in the Senate election that doesn’t show up in the FEC reports — not quite yet, anyway. That’s the money that has paid for “issue ads,” which are commercials that deal with federal candidates or elections but don’t “expressly advocate” for a candidate’s victory or loss at the polls — that don’t, for example, include such “magic words” as “vote for” or “vote against.”

Spending on issue ads need not be reported to the FEC, unless it occurs within 30 days before a primary or within 60 days before a general election. So when Keep Louisiana Working, a conservative group, ran a TV commercial several months ago mocking Landrieu for staging a Senate committee hearing in one of her commercials, the spending was not reported to the FEC.

So, too, with the ad attacking Democratic President Barack Obama’s signature Affordable Care Act that ran in Louisiana earlier this year (and earned fact-check demerits) and that was produced by Americans for Prosperity, the dark-money conservative group linked to the billionaire Koch brothers. AFP spends tens of millions of dollars nationwide to air political commercials.

The sponsors of those issue ads are required to report their spending on broadcast TV, even outside the 30- and 60-day windows, but not to the FEC. Instead, they file forms with the individual TV stations that carry the commercials. The Federal Communications Commission requires stations to post those files publicly online, but only since mid-2014 — and the FCC does not aggregate the filings. No online posting requirement applies to political advertising on cable or satellite TV, radio or the Internet.

Follow Gregory Roberts, of The Advocate Washington bureau, on Twitter, @GregRobertsDC.