Last Updated May 2, 2014 9:45 AM EDT
North Carolina primary voters go to the polls Tuesday, but it's not just residents of the Tar Heel State that have a vested interest in the outcome. Third-party groups have flooded the airwaves in North Carolina this year in an attempt to influence the critical Senate race.
Sen. Kay Hagan, D-N.C., who came into office in 2008 when Barack Obama carried her increasingly-purple state, is considered one of the most vulnerable Senate Democrats up for re-election this year. A recent New York Times/Kaiser poll shows Hagan leading her most likely Republican challenger, North Carolina House Speaker Thomas Tillis, by just two points. Recent polls of Republican voters show Tillis comfortably leading his seven GOP primary opponents, but if he doesn't win at least 40 percent of the vote on Tuesday there will be a runoff contest.
The field of candidates is crowded enough, but North Carolina voters have also heard from several outside groups. Nearly 15,000 ads at a cost of $6.3 million have already aired in the North Carolina Senate race, according to a Wesleyan Media Project analysis released this week -- and 90 percent of those were sponsored by outside groups.
The Wesleyan analysis found that outside groups have been dominating the airwaves in other states as well, including Michigan, Louisiana, Kentucky and Alaska. "Up to this point, outside groups are controlling the issue agenda in many Senate races. I almost feel sorry for the candidates as their voices are being drowned out," Travis Ridout, co-director of the Wesleyan Media Project, said in a statement.
Americans for Prosperity, the conservative political advocacy group backed by the billionaire Koch brothers, has invested the most of all the outside groups in the state, spending an estimated $8.3 million to hammer Hagan for supporting Obamacare. Meanwhile, the Karl Rove-backed super PAC American Crossroads is running ads backing Tillis and has spent more than $1.6 million so far.
It's not just conservative groups, however, jumping into the mix. The Senate Majority PAC, which aims to keep a Democratic majority in the Senate, has spent more than $3.8 million.
Both the Tillis and Hagan campaigns have grumbled about the way the outside money has influenced the race. Sadie Weiner, a spokesman for the Hagan campaign, told CBS News that outsiders "know they can count on Tillis to put their interests ahead of what's best for North Carolina, and they've spent $12 million to buy a Senator whose strings they can pull. These special interests know that they can't control Kay, and North Carolinians understand that this state cannot be bought."
Tillis, meanwhile, complained about liberals "meddling" in his race after the Senate Majority PAC ran an ad reminding voters about a controversy surrounding Tillis staffers. The ad prompted Tillis to run his own ad responding to the attacks. "Seen those ads attacking Thom Tillis? They're false," a narrator says in the ad.
"The bottom line is that voters need look no further than Thom Tillis' record to find out where he stands," Jordan Shaw, a spokesman for the Tillis campaign, told CBS News. "His record of conservative results as House Speaker is unmatched by any other candidate in this race, and I think that's why we've seen him able to establish a successful campaign thus far."
While Tillis may have a comfortable lead in the Republican primary, his opponents say it's still a competitive race for the GOP nomination -- and they have their own high-profile supporters to prove it.
Republican candidate Mark Harris has the support of former Arkansas Gov. Mike Huckabee, who told CBS News in a statement that he has been "disappointed and somewhat appalled that many of the national media have made the assumption as to who the winner in the primary will be."
Harris, Huckabee said, "represents what we need more of in Washington--people who have a long track record of community and humanitarian service."
Another Republican candidate, Greg Brannon, has the support of Sen. Rand Paul, R-Ky.. The libertarian-leaning senator will attend a rally for Brannon in Charlotte, N.C. on Monday, a day before the primary vote.
Given the legitimate competition in the primary, it may not be that surprising that groups like American Crossroads are backing Tillis, the perceived establishment candidate. There's evidence that campaign financiers are interested in knocking down the sort of "anti-establishment" candidates who lost in 2010, like Missouri Senate candidate Todd Akin.
That evidence comes from another analysis of campaign spending, released this week by the Brennan Center for Justice at NYU School of Law, which examined 12 high-dollar Republican primary races this cycle. In races with a "tea party" candidate, more money flowed to the establishment candidate, the Brennan Center found. All but two of the Tea Party candidates included in the analysis have been significantly outraised by primary opponents.
Calif. GOP Gov. candidate gets big endorsements: Republican Neel Kashkari, the former U.S. Treasury official who oversaw the bank bailout, announced some big-name endorsements this week in his bid to unseat California Gov. Jerry Brown. Former presidential candidate Mitt Romney; former Florida Gov. Jeb Bush; former California Gov. Pete Wilson; and Rep. Darrell Issa, chairman of the U.S. House Oversight Committee; all endorsed Kashkari.
Even so, the Republican has a steep hill to climb to the governor's mansion. California has a "jungle primary" system in which the two most popular candidates -- regardless of party -- advance to the general election. A survey released last week by the Public Policy Institute of California showed Brown ahead of his three Republican primary challengers; Kashkari won just 2 percent support of likely primary voters.
Landrieu keeps touting energy ties: In Louisiana, Democratic Sen. Mary Landrieu released a new campaign ad this week featuring a local shipbuilder - and former Republican official - touting the work Landrieu has done for the state's boating and energy industries.
"I have over 3,000 employees, and even though I'm a Republican and don't always agree with her, Louisiana can't afford to lose Mary Landrieu, says Boysie Bollinger, previously a state finance chairman of the Louisiana Republican Party.
Bollinger touts Landrieu's chairmanship of the Senate Energy and Natural Resources Committee, describing the post as "the most powerful position a person can have for Louisiana. It means more boats, more jobs, and more oil and gas."
Though she has prevailed in tough re-election fights before, Landrieu is considered one of the 2014 cycle's most endangered incumbents. Her likely opponent, Rep. Bill Cassidy, R-La., slammed the new ad in a statement, according to the New Orleans Times-Picayune, saying it " tells us a lot about how central a role [Landrieu] believes the government should play in our daily lives."
GOP distances itself from Grimm: New York Rep. Michael Grimm, who was indicted Monday on charges including tax fraud and employing illegal immigrants, insists he's running for re-election. His GOP colleagues seem less than thrilled about it.
The National Republican Congressional Committee is cutting Grimm out of its third "Patriot Day" fundraiser on May 21. The committee's "Patriot Program" aims to help incumbent House Republicans in competitive districts.
Meanwhile, New Hampshire GOP congressional candidate Frank Guinta gave a $2,500 contribution he received from Grimm to charity.CBS News' Jake Miller contributed to this report.