Thirty-six Senate races, $3.6 billion in total costs and one election: Here's a look at 2014 midterm spending, by the numbers. (Julie Percha/The Washington Post)

The 2014 midterm elections mark a new level of collaboration between candidates and independent groups, eroding the barrier that is supposed to separate those running for office from their big-money allies.

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The vast sums of cash raised by independent groups have reordered the political landscape, compelling campaigns to find new ways to communicate their wants and needs without officially coordinating with outside players. Such direct coordination is prohibited under 40-year-old campaign finance rules.

This year’s midterm races have seen a record amount of outside spending.

This is not how the system used to work. Just a decade ago, candidates shied away from being too closely associated with “soft money,” for reasons of appearance and for fear of running afoul of election laws.

But the rapid spread of super PACs and politically active nonprofit groups that followed the Supreme Court’s Citizens United decision has dramatically altered the climate. Political operatives are also taking advantage of the hands-off approach of a divided Federal Election Commission, which has not reexamined coordination rules in the wake of the 2010 ruling.

“There is a lot of boldness,” said Larry Norton, a campaign finance lawyer at Venable who served for six years as the FEC’s general counsel. “It’s partly a function of very sketchy rules and regulations and little enforcement. People aren’t sure where the lines are.”

In that void, candidates and independent groups have sought to bring their operations in alignment as much as possible this year.

To help allies fashion their plans, Democratic and Republican congressional committees posted detailed opposition research books and talking points about individual candidates on their Web sites. And it is now standard practice for candidates to share suggested television ad scripts and video footage online — materials that are then scooped up by outside groups and turned into television spots.

This year also saw the rise of single-candidate super PACs, flush with cash from a contender’s family and friends. More than 90 such groups sprung up to back candidates in 2014, up from 21 four years ago, according to FEC data compiled by the Center for Responsive Politics.

The closeness between candidates and their wealthy backers threatens a principle embraced by Congress after the Watergate scandal — that rich donors should not be able to give unlimited sums to an elected official.

Election Lab: See our current forecast for every congressional race in 2014

“I think the increasing degree of interaction between candidates and outside groups is rendering the candidate contribution limits meaningless,” said Paul S. Ryan, senior counsel for the Campaign Legal Center, which has filed complaints with the FEC about the widespread use of shared video footage this year.

Michael Toner, a former FEC commissioner who helped rewrite the agency’s coordination regulations after Congress overhauled campaign finance rules in 2002, said stopping candidates and independent groups from openly disseminating their plans would be impossible “unless you want to make it illegal to use information in the public sphere.”

“And I don’t know how that would be manageable or constitutional,” said Toner, a Republican campaign finance lawyer at Wiley Rein.

The interplay between both sides is only likely to increase in the 2016 elections, when personalized super PACs and other outside players are expected to be ubiquitous.

“Some of the key strategic decisions you need to make when you’re thinking about running are not only about your own campaign but, ‘Who is going to head up a super PAC for me, and how are they going to raise money?’ ” Toner said. “That’s no longer a luxury — that’s necessity.”

A robust network of groups on the left is already in place to bolster Hillary Rodham Clinton in anticipation of her second presidential run.

“You’ve seen how many resources they’ve put into developing their outside operation, and that’s for someone who is the presumed front-runner,” said Charlie Spies, a campaign finance lawyer at Clark Hill who advises GOP candidates and groups. “You move to the Republican side, and if we have an even more hotly contested primary, it’s going to be hard to generate the necessary resources” without external allies.

Independent players are poised to kick off the 2016 contest the moment this year’s elections conclude. On Wednesday, a group called Americans for Real Change that has backed former New York governor George Pataki (R) for president is set to go on the air in New Hampshire with a week-long TV cable campaign, according to ad reservations.

Many election law experts believe the current dynamic challenges one of the underlying assumptions of the Citizens United decision, which allowed unlimited independent political spending by corporations and unions based on the notion that they would not be working in conjunction with candidates and parties.

“If you are a believer in Citizens United, as I am, you actually should advocate clear rules on coordination,” said Robert Kelner, an election law attorney at Covington & Burling who advises corporations, super PACs and wealthy donors on both sides of the aisle. “If there’s no separation between the campaigns and outside groups, then the logic of the Citizens United decision really falls apart.”

The ruling has put intense pressure on the limited coordination rules that the FEC already had on the books, especially as super PACs and other big-money organizations have enlarged their roles in elections.

In 2014, such groups have gobbled up more territory that had been the traditional domain of political parties, expanding into field organizing, opposition research and data collection. They also continued to invest millions of dollars into scorching television ads, deepening the negative cast of this year’s contests.

In all, independent groups reported spending more than $500 million on congressional races this cycle, up from roughly $300 million in 2010, according to the Center for Responsive Politics. Political nonprofits that do not report all their activities spent tens of millions more.

At the same time, candidate spending has dipped, underscoring how those running for office have less control over their campaigns.

Elected officials and parties have sought to regain some of their influence by moving closer to the big-money groups.

Top advisers to Senate Majority Leader Harry M. Reid (D-Nev.) are at the helm of the Democratic group Senate Majority PAC, the biggest-spending super PAC of this year’s midterms.

The Republican National Committee and outside allies now share data from the field through an application interface created by a private firm, Data Trust, that allows them to access and update profiles of individual voters in real time.

And candidates are openly telegraphing their strategy as much as possible.

Perhaps no campaign has been as explicit as that of Thom Tillis, the Republican senatorial candidate in North Carolina. In mid-October, his campaign e-mailed an extensive strategy memo to anyone who had signed up for updates on Tillis’s Web site that listed its most pressing needs, including to “increase our spending in Asheville” and “add 1,000 gross ratings points in Charlotte.”

Tillis spokesman Daniel Keylin said the memo was aimed at donors to let them know “that we were using their money wisely and making hard budget choices.”

Such public communication is perfectly legal, election law experts said. “I do think there’s a growing feeling — and I certainly have it — that we have to rethink the whole system,” said Norton, the lawyer at Venable. “It’s bordering on just an incomprehensible system, where the rules don’t really mean anything.”

Alice Crites and Reid Wilson contributed to this report.