American Crossroads GPS, the group co-founded by Karl Rove in 2010, has been fueled by massive donations since its inception, according to recently released tax documents.

The group's tax filings reveal mostly large donations, coming from either wealthy individuals or corporations. Since the group's inception, 24 donations of over $1 million have accounted for 87 percent of its total fundraising.

Only donations of more than $5,000 are disclosed to the IRS, but among those the average value has nearly equaled $800,000. In its most recent tax documents, dating back to last June, GPS's largest donation amounted to $10 million; the second largest, $4.3 million. The group has taken 12 donations of more than $2 million and two donations of $10 million or more since its founding.

The group has raised at least $76.8 million in total.

Crossroads GPS does not disclose its donors, making it difficult or impossible to know where the money came from. The group released its tax filings to reporters on Tuesday.

Encouraged by the Supreme Court's Citizens United ruling, Rove and former Republican National Committee Chairman Ed Gillespie dreamed up two new outlets for Republican megadonors: the super PAC American Crossroads and the 501(c)4 American Crossroads Grassroots Policy Strategies (GPS). Both take in unlimited corporate donations and spend them on election ads. As a super PAC, American Crossroads discloses its donors to the Federal Election Commission; Crossroads GPS, as a "social-welfare" group under IRS code, keeps its donors secret but is required by the IRS to expend less than half of its effort on direct electoral politics.

To maintain that balance, Crossroads GPS has spent $17.1 million on campaign politics and $27.1 million on "grassroots issue advocacy"-a category that includes issue ads that can mention a candidate, and even express an opinion of that candidate, as long as the IRS does not deem them tantamount to election advertising.

The Campaign Legal Center and other advocates have called for an IRS audit of Crossroads GPS to determine whether a majority of its activity crosses the campaign-politics boundary and violates the requirements for "social welfare" tax-exempt status under section 501(c)4 of the U.S. tax code.

The group has also donated $15.9 million to related tax-exempt, GOP-aligned groups. The largest beneficiaries have been Americans for Tax Reform (which received $4 million), the National Federation of Independent Business ($3.7 million), the Center for Individual Freedom ($2.75 million), and National Right to Life ($2 million).

While Crossroads GPS does not control how that money is spent, and while those groups do engage in political activity, those groups are subject to the same stipulations over campaign-politics and issue-advocacy.

Together, American Crossroads and Crossroads GPS have spent at least $94.5 million since their creation. The 501(c)4 Crossroads GPS has spent more than twice its super PAC counterpart: Crossroads GPS has spent a total of $64.7 million, while American Crossroads has spent $29 million.

This month, Crossroads GPS began running its first anti-Obama ad of 2012, attacking the president for high gas prices.