Donors can contribute unlimited amounts to candidates' super PACs, and they have. Here are the nine Republicans who you need to know as their donations shape the primaries.
The billionaire brothers made their fortunes in fracking, and along with their wives, are sending $15 million to boost fellow Texan Ted Cruz's presidential campaign.
Mercer, a reclusive hedge-funder from New York, was one of the top Republican givers in 2012 and 2014. And he's betting big -- $11 million big -- on Cruz, a senator who managed to raise $38 million despite having weak connections with the donor class.
Mercer also gave $250,000 to Bobby Jindal, and in a somewhat unusual move, reassigned $500,000 that he gave to Cruz's super PAC to Carly Fiorina's.
Toby Neugebauer: $10 million
The Mercers and Wilks are two of three families controlling their own pro-Cruz super PAC. Toby Neugebauer, the son of a congressman and a Houston oil investor, controls another with his $10 million.
Kelcy Warren: $6 million
Warren, who became a billionaire through piping, is one of two Dallas men bankrolling the majority of Rick Perry's super PAC.
Darwin Deason: $5 million
Deason is the other Dallas man betting on Perry.
Diane Hendricks: $5 million
A roofing billionaire, Hendricks shares a home state with Wisconsin Gov. Scott Walker, and has long supported his campaigns. The money went to Walker's PAC Unintimidated, which has raised $20 million.
Marlene Ricketts: $5 million
Walker's other big family is the Ricketts of the Midwest. Marlene is married to Joe Ricketts, who founded TD Ameritrade, and is the mom of Todd, the Walker campaign's finance director.
Norman Braman: $5 million
Braman is reportedly willing to invest $10 million of his own money to boost the campaign of Marco Rubio, his mentee in Miami.