Maine's U.S. Senate race is a battle between not two, but three candidates vying to replace retiring Senator Olympia Snowe: Republican Charlie Summers, Democrat Cynthia Dill, and former Governor Angus King, a left-leaning independent. Despite outside groups like the U.S. Chamber of Commerce spending millions attacking King, he retains a sizable lead -- but the complex, multi-million dollar web of outside spending has made Maine's U.S. Senate race one of the most interesting in the country.

The three-way, multi-party race is unique this election cycle, and big-money groups enabled by the U.S. Supreme Court's decision in Citizens United v. FEC have calculated how much to tear down -- or in one case, support -- candidates running against their chosen favorite. Supporters of the Republican, Summers, have invested heavily in the race, not only tearing down King but also pushing some of his supporters towards the Democrat, Dill -- with the expectation that Summers could get a plurality of votes by splitting King's lead. In one of the most cynical political ploys this election cycle, one group, funded entirely by conservative donors, has even been running ads in support of the Democrat. The national Democratic party, meanwhile, has refused to endorse the Democratic candidate and has provided minimal support, apparently expecting that if King wins he will caucus with the Democrats [3].

In total, Maine's Morning Sentinel [4] estimates that outside groups have spent $5.48 million influencing the Maine's Senate race, more than all candidates combined, and have purchased 60 percent of all ads in the race so far.

"Maine Freedom PAC" Backs Dem with Republican Leadership and Money

In the post-Citizens United world, it can be difficult to discern the motives of the innocuously named Super PACs and mysterious dark money nonprofits spending hundreds of millions in elections. But few groups appear to be as cynical and misleading as the Maine Freedom PAC [5], a Washington D.C.-based Super PAC apparently led and funded by Republicans, but spending to support a Democrat. So far Maine Freedom has spent $359,000 [6] in the race.

The group's leadership includes Michael Adams [7], who is the general counsel of the Republican Governor's Association (and who was formerly the RNC's in-house general counsel), and its assistant treasurer also has ties to the RGA and other Republican groups. The group also used a Republican-linked firm for its ad buys.

Adams has described [8] his Super PAC as "a bipartisan coalition of people who live in Maine or love Maine or both, and who are focused on getting the facts out about the candidates for U.S. Senate," but their funding seems to come from only one side of the political spectrum.

Their largest backer [9], Paul Coulombe, owns the Maine-based White Rock Distillery and has given the group $200,000 since its creation earlier this year. His other political contributions this year include donations directly to the Summers campaign and Maine's Republican Party.The SuperPAC received $100,000 each [10] from Liberty Media Owner John C. Malone and Quantlab Financial CEO Edward Bosarge. Bosarge is a major contributor [11] to the Maine Republican Party while Malone sits on the board of the Koch-founded Cato Institute [12], a leading libertarian think tank, and has also donated heavily to [13] the Maine Republican Party, and Mitt Romney's presidential campaign.

The group's ads give the appearance of supporting the Democratic candidate, Dill, and attacking King, but appear masterfully designed [14] to repel Republicans from King while drawing Democrats to Dill. One ad [15] from August calls both King and Dill "reliable Obama allies on health care and taxes," but praises Dill as "a champion of marriage equality and stronger gun laws."

Maine Freedom remains the only outside spender to promote Dill, but she has denounced their support and labelled it "cynical" [16]. Dill is currently polling at just over 10 percent [17] of the popular vote, at this point, so any group supporting her would likely benefit Summers by drawing liberal voters away from King and narrowing his lead.

Crossroads GPS, Chamber of Commerce, NRCC Attack King, Ignore Dems

The most direct attacks in the Maine Senate race have come from Crossroads GPS [18] and the U.S. Chamber of Commerce [19], two dark money groups that have spent tens of millions supporting Republicans (or attacking Democrats), but do not disclose their donors. In the Maine race, these groups have largely ignored the Democratic candidate and aimed their fire at the frontrunner, independent candidate King.

The Chamber has been King's biggest opponent [20] in the Maine Senate race, buying $1.3 million of ads against him, more than the amount spent by the Dill and Summers campaigns, combined. The Chamber has labeled him "the king of spending" [21] due to an alleged budget shortfall during his term as Governor. The Chamber endorsed Summers [22], but have not mentioned him in any of their ads, apparently calculating that the best plan to secure victory for Summers is to pull votes away from King [23].

Last week, Crossroads GPS echoed the Chamber's claim in their own $300,000 ad buy [24], which repeats the accusations [25] of the Chamber nearly verbatim. GPS has recently run a second ad [26] attacking King because he allegedly "slashed funding for our schools" and made money off of a windmill company that he recommended for taxpayer funding: "King made sure he could live like...a king." According to Maine's Kennebec Journal [27], the claims in that latest ad are false -- education spending overall increased during King's tenure, and the claim that he benefitted from government loans to his windmill company was called "maliciously" false.

The National Republican Senatorial Committee has also invested $1.3 million [20] in the Maine race. The group's most recent ad [28] made the same "maliciously" false claims as Crossroads GPS [18] about King's windmill company. An earlier ad [29] attacked King's independence, suggesting his success in the race was attributable to the machinations of Chuck Schumer and the Democratic Party, who according to the ads "shoved aside more liberal candidates" and "betray[ed] their principles to ensure King would caucus with the Democrats." The ad claimed "Maine deserves better than smoke-filled back-room deals."

King Fights Back with Godzilla and Americans Elect

King has fought back against the outside ads directly, with his own counter-ad [30] featuring shots from the movie "Godzilla." King warned of the coming ads from "some folks from away" who will depict him as a monster, but tells voters that they know the real Angus King (and his mustache) from his time as governor.

However, King has received sizable help from "some folks from away" himself. As an independent he does not have the logistical or financial support of a political party, but he has benefitted from over $1.4 million in "independent" expenditures [31] from a Super PAC connected to Americans Elect, a group initially designed [32] to promote a third-party moderate candidate for president via an online primary. That effort failed [33], but three of its deep-pocketed backers [34] have chipped in to focus almost exclusively on the Maine race.

While American's Elect is promoting an independent, and gained national attention earlier this year with its promise to revolutionize politics, its tactics in the Maine race reflect a mainstream Super PAC strategy: like most Super PACs, the one supporting King is sustained by a small group of very wealthy donors (billionaires Michael Bloomberg, Peter Ackerman, and John Burbank [35]), and like most Super PACs [36]. There is also overlap in personnel between the Super PAC and King's campaign: a former chairman of American's Elect is now chairing King's Senate campaign [35].

The group has run ads that promote King's independent [37] reputation and claim he will "bring business and government together, and take the best solutions from both parties." They have also released ads and mailers targeting the Republican candidate Summers.

DSCC Provides Air Support, But Not Clear for Whom

Even the Democratic Party's motivations are not entirely clear in the Maine race. The party has not endorsed a candidate in the race and Dill has not received any financial or technical support [38], perhaps because boosting her poll numbers would hurt King's chances of victory. The Democratic Senatorial Campaign Committee has spent $1.7 million [39] in Maine, but not necessarily to support Dill -- all of their ad buys have attacked Summers [40] without supporting an alternative.