Senate Majority Leader Mitch McConnell (R-KY) and fellow GOP leaders talk to reporters after the weekly Republican policy luncheon at the U.S. Capitol November 10, 2015 in Washington, DC. Chip Somodevilla/Getty Images

The group aired more than 12,400 television advertisements, according to a Center for Public Integrity analysis of data provided by advertising tracking firm Kantar Media/CMAG, which monitors broadcast and national cable — but not local cable — TV ads. That represented about one in every seven spots during the U.S. Senate race. According to the new tax filing, the Kentucky Opportunity Coalition spent $7.6 million on “direct and indirect political campaign activities” in 2014 — about 41 percent of the nearly $18.7 million it spent overall. Advocating for or against candidates cannot be the “primary purpose” of such nonprofit groups. Not counted in that sum: the nearly $9 million Kentucky Opportunity Coalition spent to “influence policymaking outcomes,” which included numerous TV ad buys praising McConnell for “standing up for Kentucky coal” and fighting back against President Barack Obama’s “war on coal.” Nor does it include the additional $1.35 million the Kentucky Opportunity Coalition issued in grants to other nonprofit groups active in Kentucky’s U.S. Senate race — namely the $1 million it gave to the U.S. Chamber of Commerce and the $350,000 it contributed to Crossroads GPS, a nonprofit associated with veteran GOP strategist Karl Rove. Like other “social welfare” nonprofits organized under Sec. 501(c)(4) of the U.S. tax code, the Kentucky Opportunity Coalition is generally not required to reveal the names of its financial supporters. It must, however, list the amounts given by big donors. In 2014 alone, three unknown megadonors alone accounted for more than 60 percent of the $15 million the Kentucky Opportunity Coalition raised. The largest donor contributed $5 million. Another gave about $3.4 million. A third gave $1 million. One known donor to the Kentucky Opportunity Coalition? Crossroads GPS, the conservative nonprofit that also received money from the pro-McConnell group last year. Crossroads GPS told the IRS it last year gave the Kentucky Opportunity Coalition $390,000, as the Center for Public Integrity reported earlier this week.