American Chemistry Council spent more than $300,000 on ads supporting Eric Cantor; Image credit American Chemistry Council

Exactly halfway through primary season — as voters head to the polls Tuesday in Maine, Nevada, North Dakota, South Carolina and Virginia — it’s now obvious just how much a driver of outside spending the GOP’s family feuds have been.

Of the more than $107 million worth of independent expenditures tabulated by Sunlight’s Real-Time FEC tool, more than $80 million have been focused on Republican primaries. Third-party groups have combined to spend just under $47.4 million attacking Republican candidates and $33.06 million supporting them. That’s compared to $15.4 million spent opposing Democratic candidates for federal office and nearly $10.8 boosting liberals.

However, some of the most heavy-hitting outside groups were still sitting on millions in their campaign war chests at the start of primary season. Per campaign disclosures from the beginning of May, nine different outside groups had $5 million or more in the bank. The national parties’ congressional accounts were still loaded, with the DCCC counting more than $43 million on hand compared to the NRCC’s $32 million. The parties’ Senate committees do not file their reports online.

While none of Tuesday’s primaries have attracted millions in outside dollars or the national media attention that marquee match-ups in Kentucky or Mississippi did, several prominent Republicans are looking to squelch challenges from the right.

In Virginia, House Majority Leader Eric Cantor faces economics professor Dave Brat in the Old Dominion’s 7th District. Though a Daily Caller poll shows the dark horse candidate — who has won the support of small government icon Grover Norquist — may be cutting into Cantor’s lead, the incumbent remains the odds-on favorite to keep his seat in the conservative central district.

Brat is operating at a severe cash disadvantage. Cantor’s campaign raised more than $5.7 million to the rookie candidate’s $230,000, and the incumbent has gotten some advertising help from political allies.

The American Chemistry Council, a chemical manufacturers’ trade group lobbying Congress to overhaul the 1976 Toxic Substances Control Act, has been the biggest outside player in the race, spending $308,731 in May alone on TV ads supporting Cantor.

In South Carolina, although Republican Sen. Lindsay Graham may be a favorite punching bag for his party’s conservative flank, all signs point to the two-term senator avoiding a runoff against a crowded Republican field.

Graham, who faces six other candidates in Tuesday’s primary, got a boost from conservative nonprofit Citizens for Responsible Energy Solutions. The organization, run by a lobbyist at Civitas Public Affairs, supports conservatives in favor of renewable energy and reducing pollution, according to the group’s website.

The veteran Palmetto State senator has kept an aggressive pace on the fundraising scene, attending parties from Kiawah Island, S.C., to Manhattan en route to raising at least $6.4 million. As of May 21, Graham’s campaign had spent $7.1 million. Richard Cash, number two on the fundraising circuit, had raised a paltry $750,000.

Few Democratic primaries have attracted large outside expenditures. One of the priciest is the liberal-on-liberal battle for Maine’s sprawling 2nd District. The seat, which Rothenberg Political Report considers “Democrat favored,” is open as Democratic Rep. Mike Michaud runs for governor.

The race centers on Troy Jackson, a union-backed state senator and logger, who has been targeted by the League of Conservation Voters for his “anti-environmental voting record” in the state legislature. The LCV, which has spent $131,704 on the race, favors state Sen. Emily Cain, who also has the backing of Women Vote!, the super PAC affiliated with the pro-choice organization Emily’s List. Women Vote! has spent just under $90,000 on ads supporting Cain.