One of the country’s largest oil refiners, Andeavor, contributed $1 million in both 2016 and 2017 to One Nation, a dark money group with close ties to Senate Majority Leader Mitch McConnell (R-KY), according to voluntary disclosures on the company’s website. Since One Nation is not required to disclose its contributors, Andeavor’s disclosure of its contributions makes it one of the only known donors to the politically active nonprofit.

Andeavor’s contributions may have been used to support One Nation’s efforts to influence elections. On the webpage where Andeavor voluntarily discloses information about its political and advocacy contributions, the oil refiner acknowledges that some portion of its contributions to groups like One Nation “may be used for the purposes of lobbying or political expenditures.” A spokesperson for Andeavor told the Texas Observer in April 2018 that since it “operates in a highly regulated and often politicized environment,” the company believes it has a responsibility to “advocate for sound energy policies and actively engage in the political process to ensure we continue to operate in a healthy business environment.”

In 2016, when Andeavor, then known as Tesoro, contributed to One Nation, the nonprofit spent more than $63 million overall, including $3.4 million it reported to the FEC as independent expenditures and $21.7 million in contributions to the Senate Leadership Fund, a super PAC. In addition, One Nation disclosed spending $33.3 million on “grassroots issue advocacy,” a likely reference to ads that did not explicitly call for the election or defeat of a candidate. According to data analyzed by the Center for Responsive Politics and the Wesleyan Media Project in an August 2016 report, the number of ads One Nation purchased in 2016 alone was enough to rank the nonprofit as 26th on a list of the top 50 outside groups between 2000 and 2016.

The group’s massive ad spending was largely made possible by seven- and eight-figure checks, including the $1 million provided by Andeavor. According to One Nation’s 2016 tax return, which reveals contribution amounts without identifying information about donors, 15 anonymous donors gave at least $1 million to the group, including three who contributed at least $10 million each.

Other than Andeavor, few other 2016 donors to One Nation are publicly known. Crossroads GPS, a politically active nonprofit that also does not disclose its donors, previously reported on its 2016 tax return that it gave One Nation $11.75 million that year. Crossroads and One Nation are both run by Steven Law, Sen. McConnell’s former chief of staff, who also runs the Senate Leadership Fund. The American Health Care Association, a federation of affiliate state health organizations, also disclosed contributing $200,000 to One Nation in 2016.

One Nation’s 2017 tax return is not yet publicly available, but the group reportedly raised $16.7 million that year, which presumably includes the $1 million Andeavor disclosed contributing. The McConnell-tied group only posted one press release on its website over the course of 2017, which promoted a radio ad praising then-Sen. Luther Strange (R-AL), who would soon face a primary from former judge Roy Moore. According to the Birmingham News, One Nation planned to spend $385,000 on issue ads boosting Strange during the summer of 2017. Strange, who had been appointed to the the seat after Jeff Sessions was named attorney general by President Trump, ultimately lost the nomination to Moore in September 2017.

Andeavor has not yet posted its voluntary political contribution disclosures for 2018, so it is unknown if the company has continued to fund One Nation. Described by USA Today as “the best-financed group in the McConnell orbit,” One Nation has reportedly spent at least $40 million during the 2018 election cycle, including $27 million on TV and radio ads as well as more than $1.7 million on Google ads. One Nation targets almost all of its ad spending in states with competitive Senate races, either praising Republican candidates or criticizing Democrats. But since the ads do not directly call for votes for or against any of the candidates, none of the group’s 2018 spending has been reported to the Federal Election Commission (FEC). The Senate Leadership Fund has also reported receiving $12.8 million from One Nation in 2018.

In April 2018, when One Nation and the Senate Leadership Fund’s fundraising numbers were provided to Politico, along with the numbers for Crossroads GPS and the super PAC American Crossroads, Law touted Sen. McConnell’s efforts to help raise money, saying the senator had done a “huge amount” of travel, meetings and phone calls. Law told Politico that donors were focused on “holding a senate majority as a firewall.” According to FEC records, Tesoro Companies, a subsidiary of Andeavor, contributed $1 million in February 2018 to the Senate Leadership Fund while Andeavor’s PAC gave $30,000 in September 2018.

During the same time period when Andeavor and its subsidiary were contributing large sums to a nonprofit and super PAC closely-tied to the top Republican in the Senate, the company spent significant money on lobbying the federal government, including the Senate. According to the Center for Responsive Politics, Andeavor’s lobbying expenditures spiked significantly in 2017, rising to $2.7 million from the $1.1 million the company spent in 2016. The most common issue named in the company’s lobbying reports that year was taxes. The tax cut legislation passed by Congress and signed by President Trump in December 2017 was reportedly very good for Andeavor’s bottom line, producing a benefit of $918 million in the fourth quarter of that year.

Andeavor’s contributions to One Nation are only known because the company made an affirmative decision to disclose them. Most of the group’s donors, which could include other special interests with business before the Senate, remain secret except to the operatives behind the nonprofit and, perhaps, the politicians who help the group raise money.