Senate campaign committees tapped two familiar hands to lead their independent expenditures this cycle — a high-stakes gig that controls tens of millions of dollars in spending for 2012 races.

But these Senate money managers will confront new challenges this cycle as outside group and super PAC spending increasingly compete for air time.

The Democratic Senatorial Campaign Committee hired Martha McKenna as its IE director, while the National Republican Senatorial Committee picked Mike DuHaime to serve as director and Greg Strimple to serve as strategist for its outside spending arm.

The Senate stakes are high this cycle, and party operatives from both sides agree the chamber is in play. Democrats will attempt to protect a 53-seat Majority, while Republicans try to take control of the Senate by winning three or four seats.

Since the landmark McCain-Feingold campaign finance legislation, independent expenditure directors have played a pivotal role in choosing which Senate races receive financial attention. The committees put incredible trust in these operatives because communication is illegal: The committees cannot coordinate with the IE arm, and the IE arm cannot communicate with individual campaigns.

“The party committees raise a substantial amount of money, and the vast majority of those funds get spent on the IE program,” said Brian Smoot, the Democratic consultant charged with directing the DSCC’s 2010 IE unit. “Since you cannot coordinate with the campaign or the rest of the DSCC, it is important to have a good understanding of each race.”

But the role of these IEs has evolved since the Supreme Court’s landmark Citizens United ruling in 2010.

For most of the past decade, these IE arms were the best-funded game in town for Congressional races. In 2010, the DSCC spent $40.1 million in IEs and the NRSC spent $25.9 million in IEs, according to the campaign finance disclosure website OpenSecrets.

But in wake of the high court’s ruling, anyone can try to contend with the IE’s cash largesse by starting a super PAC.

“Obviously, you’re not allowed to coordinate with them, but you have to keep your eye on them,” said Brian Nick, a former NRSC chief spokesman. “It’s a factor that’s increasing that didn’t exist to this extent a couple cycles ago. Certainly there were some third-party groups, but nothing like the scope of third-party groups now spending at this level.”

For example, the conservative American Crossroads and its sister organization, Crossroads GPS, spent more than $40 million on Senate-related advocacy last cycle. This cycle, Democrats launched their own outside IE arm, Majority PAC, to contend with Crossroads’ spending blitz.

Much like in previous cycles, both McKenna and DuHaime are familiar faces within their respective committees. The House campaign committees have not yet released who will direct their respective IE units.

McKenna oversaw two Senate cycles as the DSCC’s political director in 2008 and 2010. She also boasts more than a decade of work with EMILY’s List. The DSCC has gone to great lengths this cycle to promote its bevy of female challengers and incumbents, DSCC Executive Director Guy Cecil suggested it was fitting to pick an IE director with experience in women’s candidates.

“Martha McKenna has helped oversee some of the best Democratic campaigns of the last decade,” Cecil said. “Martha’s experience at EMILY’s List and electing women candidates across the country will be especially critical given the historic opportunity we have to elect more Democratic women to the Senate than ever before.”

DuHaime also brings recent Senate experience to the table from running the NRSC’s IEs last cycle. But he is perhaps best known for advising New Jersey Gov. Chris Christie’s campaign in 2009 and managing former New York City Mayor Rudy Giuliani’s bid for president in 2008. He also served as the Republican National Committee’s political director in the 2006 cycle.

“Mike is one of the best operatives in the Republican party today and we are fortunate to have him,” NRSC Executive Director Rob Jesmer said. “We would not have picked up seven seats last cycle without him, and [NRSC Chairman] Sen. [John] Cornyn is confident he will do great work again in 2012.”

In addition to DuHaime, Strimple — a pollster by trade — will serve as the strategist for the NRSC’s IE unit. Strimple also advised Christie’s 2009 victory. He was a senior adviser for Sen. John McCain’s (Ariz.) 2008 presidential bid and served on Sen. Mark Kirk’s (Ill.) 2010 campaign.

“Greg has a record of being an integral part of winning campaigns in some very tough places for Republicans,” Jesmer said. “His polling last cycle in Sen. Kirk’s race was dead on; more importantly his analysis provided the road map for a Kirk victory.”

The stakes are high for both units to execute their party’s message in each race without actually coordinating with the NRSC or the DSCC. A misfire can quickly blow up in a committee’s face, even if it legally had no control over the advertisement.

Most famously, in the 2006 cycle, three simple words in an RNC IE spot ignited charges of racism in the Tennessee Senate race between then-Rep. Harold Ford Jr. (D) and now-Sen. Bob Corker (R).

“Harold, call me,” says a blonde actress who pretends she met Ford at a Playboy mansion party.

The controversial spot put the NRSC, RNC and Corker on defense — even though none of those parties had any role in writing the advertisement or approving it for the airwaves. Eventually, Corker publicly called to take the ad off the air, and RNC Chairman Ken Mehlman was forced to defend a spot he had no part in creating on broadcast television.

“That was an IE ad,” a Senate Republican operative recalled. “The campaign couldn’t do anything about it … It got very uncomfortable for everybody trying to explain.”