The top priority for Republican presidential candidates right now isn't lining up voters—it's locking down donors. The big money men and women will determine how close each of the two dozen or so contenders can get to the White House. And as a result of court rulings that eliminated limits on contributions in support of candidates, one or two key mega-donors can turn a long-shot into a serious candidate. Just ask Newt Gingrich or Rick Santorum. In 2012, the casino magnate Sheldon Adelson gave $15 million to a super PAC backing the former House speaker, while Foster Friess, a deep-pocketed investor, almost single-handedly propped up Santorum's bid long enough for him to give Mitt Romney his most serious challenge for the GOP nomination.

Friess is backing Santorum again if he runs, but with Gingrich foregoing the race, Adelson is up for grabs. So are a number of other conservative billionaires who GOP contenders are hoping to secure as their patrons. (Hillary Clinton, of course, already has all the deep-pocketed donors she'll need to be competitive on the Democratic side; none of her prospective rivals appears to have secured a billionaire of their own.) Here's a guide to the biggest Republican mega-donors and the candidates they are funding—or might fund—in the 2016 campaign.


David Koch (Carlo Allegri/Reuters)

Charles and David Koch

Estimated net worth: $100 billion

How they made they money: Koch Industries, based in Kansas, is the country's second-largest private company. It began as an oil refinery and has since expanded into many other fields.

Who they're backing: The Koch brothers have historically stayed neutral in the presidential primaries, but that may change this time around. David Koch appeared to tip his hand Monday at a GOP fund-raiser by predicting that Scott Walker would be the nominee, The New York Times reported. But he backtracked almost as soon as the news got out, insisting he wasn't endorsing the Wisconsin governor. Brother Charles then told USA Today that five Republican contenders could get their support: Walker, Jeb Bush, Ted Cruz, Rand Paul, and Marco Rubio. But he said the family might contribute to multiple candidates before settling on a single pick.


Sheldon Adelson (John Locher/AP)

Sheldon Adelson

Estimated net worth: $29.1 billion

How he made his money: Casinos

Who he's backing: Formally, no one yet. But he's repeatedly been linked to Rubio in recent weeks. Politico reported that Adelson has told friends that the first-term Florida senator is "the future of the Republican Party." Adelson is also pleased with Rubio's strong support for Israel. Still, the billionaire is hosting several GOP hopefuls this weekend in Las Vegas, at an annual event often described as an "audition" for his support.


Foster Friess (Eric Gay/AP)

Foster Friess

Estimated net worth: $530 million as of 2012, according to the Wealth-X research firm

How he made his money: Mutual-fund investing

Who he's backing: Friess is boosting Santorum again, but the bigger questions are whether the former Pennsylvania senator will even run, and if he does, how competitive he'll be. After faring surprisingly well in 2012, he is preparing for another try, but he has not drawn much attention as the newer and bigger names in the race.


Paul Singer

Estimated net worth: $1.92 billion

How he made his money: Hedge funds

Who he's backing: Like Adelson, Singer has also been linked to Rubio. But the hedge-fund billionaire who backed Mitt Romney and Rudy Giuliani in the last two campaigns "has not yet settled on any one candidate," a spokeswoman told me.


Robert Mercer

Estimated net worth: Unknown, but he reportedly earned $100 million or more annually between 2011-2013

How he made his money: Renaissance Technologies, a hedge-fund company

Who he's backing: Ted Cruz. Mercer is Cruz's big catch so far. According to The New York Times, he is "believed to be the main donor behind" four super PACs that have bankrolled the Tea Party star's early campaigning. Like Koch, however, the lower-profile Mercer has the potential to be a liability: His hedge fund has been under investigation for owing as much as $6 billion in unpaid taxes.


Woody Johnson (Jordan Strauss/AP)

Woody Johnson

Estimated net worth: Unknown, but he's the owner of the New York Jets, a franchise whose value has been estimated at $1.38 billion

How he made his money: His great-grandfather co-founded Johnson & Johnson, and Woody now runs his own investment firm.

Who he's backing: Jeb Bush. Johnson was an early Romney backer in 2012, and along with Mel Sembler and several others in the GOP nominee's camp, he switched to Bush once Romney decided not to run in 2016. His move was seen as a blow to Chris Christie, who is competing with Bush for establishment support.


Norman Braman (Lynne Sladky/AP)

Norman Braman

Estimated net worth: $1.89 billion

How he made his money: Selling cars

Who he's backing: Marco Rubio. The former Philadelphia Eagles owner could be Rubio's sugar donor in the same way Adelson was for Gingrich and Friess was for Santorum. Politico reported that Braman could spend between $10 million and $25 million funding Rubio's super PAC, and that his support is as much about a 11-year-old grudge he holds against Bush as it is about Rubio.


Ken Langone (Mark Lennihan/AP)

Ken Langone

Estimated net worth: $2.7 billion

How he made his money: He co-founded Home Depot.

Who he's backing: Chris Christie. The New Jersey governor is lagging in early polls and has watched some of his wealthy backers sign on with other candidates. But Langone, who tried to coax him into the presidential 2012 race, remains firmly in his corner. He told the Wall Street Journal that he was a "one-trick-pony" for Christie in 2016, so if he doesn't run, Langone may sit out the primary season.


Joe Ricketts (Nati Harnik/AP)

Joe Ricketts

Estimated net worth: $1.67 billion

How he made his money: He co-founded Ameritrade, which is now TD Ameritrade, the online stock-trading giant.

Who he's backing: No one, officially. Ricketts, whose family also owns the Chicago Cubs, spent more than $20 million since 2010 on his anti-Obama, Ending Spending super PAC. He's been a big supporter of Scott Walker in neighboring Wisconsin, but a source close to the billionaire says he has committed to anyone yet in the 2016 race. His son Pete was elected governor of Nebraska last year.


Peter Thiel (Yuri Gripas/Reuters)

Peter Thiel

Estimated net worth: $2.2 billion

How he made his money: He invested early in Facebook and co-founded PayPal. Thiel now runs Founders Fund, a venture capital firm.

Who he's backing: Thiel was a big backer of Ron Paul in 2012, and the big question now is whether he'll support his son, Rand. The two men met last year, but there's no word yet as to whether Thiel is on board with the Kentucky senator for 2016.