WASHINGTON -- The demolition machine known as Restore Our Future, the super PAC backing the presidential bid of Mitt Romney, pulled in $8.6 million in March, bringing its total raised above $50 million.

The super PAC, which can raise unlimited contributions from corporations, unions and individuals, was instrumental in knocking off Romney's competitors by drowning them out with negative advertisements at crucial moments.

Newt Gingrich, the first candidate to pose a true threat to Romney, has been the target of $18.4 million in negative attacks over the course of the campaign; and Rick Santorum, who was Romney's closest competitor, was hit with $20 million from the massive super PAC.

Many of the March donors to Restore Our Future were repeat donors coming back to give even more to help out Romney's efforts to beat back Santorum, who suspended his campaign on April 10.

The biggest single contribution in March, of $1 million, came from a company called Huron Carbon LLC, which shares the address of William Koch's company Oxbow Carbon. Koch, through personal giving and through Oxbow Carbon, had previously given $1 million to the super PAC.

Hedge fund honcho Kenneth Griffin, who made waves a month ago when he stated that the very wealthy had "insufficient influence" in politics, is clearly trying to increase that influence with his giving. In March, Griffin -- who, along with his wife, had previously given $200,000 to Restore Our Future -- chipped in an additional $850,000, taking his total above $1 million.

Both J.W. Marriott and Richard Marriott, the scions of the well-known hotel company that bears their name, each chipped in an additional $250,000. They have each now given $1 million to the pro-Romney super PAC.

The CEO of New Balance Shoes, James Davis, contributed another $500,000 to the super PAC, pushing his total giving to $1 million. Another $500,000 came from the Dallas industrialist Harold Simmons, who is in competition with the casino billionaire Sheldon Adelson for the distinction of biggest super PAC donor of the cycle.

Corporations, which have been enabled to donate to independent groups like Restore Our Future by the Supreme Court's 2010 Citizens United ruling, accounted for $1.825 million of the super PAC's March haul.

Aside from Huron Carbon LLC, the other big givers among corporations include Seaspray Partners LLC ($400,000), Fair Oaks Finance LLC ($250,000) and Mischer Investments ($100,000).

Related on HuffPost: