(CNN) Jeb Bush has built a formidable campaign with top-flight staff in all the early states and announced a respectable third-quarter haul of $13.4 million. But with only $10 million cash-in-hand, the big question is whether he can sustain it.

Bob 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. 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.

Bob 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. 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.

From left, Dan and Farris Wilks are billionaire brothers who made their fortunes in fracking. Along with their wives, they are sending $15 million to boost the campaign of fellow Texan Ted Cruz.

From left, Dan and Farris Wilks are billionaire brothers who made their fortunes in fracking. Along with their wives, they are sending $15 million to boost the campaign of fellow Texan Ted Cruz.

Kelcy Warren, who became a billionaire through piping, is one of two Dallas men bankrolling the majority of Rick Perry's super PAC.

Kelcy Warren, who became a billionaire through piping, is one of two Dallas men bankrolling the majority of Rick Perry's super PAC.

Diane Hendricks, a roofing billionaire, shares a home state with Walker and has long supported his campaigns. She has donated to Walker's PAC Unintimidated, which has raised $20 million.

Diane Hendricks, a roofing billionaire, shares a home state with Walker and has long supported his campaigns. She has donated to Walker's PAC Unintimidated, which has raised $20 million.

New York investor Paul Singer, who gave $10.5 million to outside groups in 2014, has not donated any money yet this election.

New York investor Paul Singer, who gave $10.5 million to outside groups in 2014, has not donated any money yet this election.

Silicon Valley angel investor Peter Thiel has not committed to donating to anyone yet. According to OpenSecrets, he has given more than $5 million in political donations since 2004.

Silicon Valley angel investor Peter Thiel has not committed to donating to anyone yet. According to OpenSecrets, he has given more than $5 million in political donations since 2004.

The Koch brothers -- Charles, left, and David -- are known for making significant financial contributions to conservative presidential candidates. They have reportedly not donated to any 2016 super PACs so far.

The Koch brothers -- Charles, left, and David -- are known for making significant financial contributions to conservative presidential candidates. They have reportedly not donated to any 2016 super PACs so far.

Casino magnate Sheldon Adelson, the GOP's top giver in 2012, has not given any money to Republican candidates' allied groups for the 2016 election.According to OpenSecrets , he spent almost $92 million on conservatives in the 2012 election.

As presidential candidates gear up for the 2016 election, their super PACs -- which can accept unlimited donations as long as they don't coordinate spending with the campaign -- eye wealthy businessmen who can donate large sums of cash. Here's a look at well-known donors who have given money to conservative presidential campaigns in the past.

As presidential candidates gear up for the 2016 election, their super PACs -- which can accept unlimited donations as long as they don't coordinate spending with the campaign -- eye wealthy businessmen who can donate large sums of cash. Here's a look at well-known donors who have given money to conservative presidential campaigns in the past.

His fundraising total is in the neighborhood of the number that his allies and donors had expected for the third quarter, as he has struggled to get attention in the shadow of Donald Trump . Financial backers of Bush -- many of whom chose the former Florida governor because they thought he was the most formidable contender -- have been dismayed by his standing in the polls in recent months, despite his breakneck pace of campaigning.

With his campaign coffers flush and with ads on the air in New Hampshire introducing his record to voters, they expected him to be up in a far stronger position in the polls -- not competing with Trump and other outsider candidates like Carly Fiorina and Ben Carson

Bush raised more money in the third quarter than rivals Marco Rubio or Ted Cruz , but both have more money than him in the bank -- Rubio with $11 million, Cruz with $13.5. And they have fewer mouths to feed with smaller campaign operations.

Still many Bush allies have said in interviews that while they would like to see progress, they are dealing with a new and unfamiliar phenomenon in Trump. That is why the campaign has spent so much time and money contacting voters in early states like Nevada and New Hampshire.

In interviews, Bush donors have said that while Bush has had his share of gaffes, he has been improving on the campaign trail. They see Rubio's inexperience -- and the inevitable comparisons to Barack Obama -- as a major vulnerability in running a general election race against Hillary Clinton

Photos: Who's running for president? Photos: Who's running for president? Ted Cruz, Donald Trump, John Kasich, Hillary Clinton and Bernie Sanders, Hide Caption 1 of 6 Photos: Who's running for president?



"So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Businessman Donald Trump announced June 16 at his Trump Tower in New York City that he is seeking the Republican presidential nomination. This ends more than two decades of flirting with the idea of running for the White House."So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Hide Caption 2 of 6 Photos: Who's running for president?



"These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Sen. Ted Cruz of Texas has made a name for himself in the Senate, solidifying his brand as a conservative firebrand willing to take on the GOP's establishment. He announced he was seeking the Republican presidential nomination in a speech on March 23."These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Hide Caption 3 of 6 Photos: Who's running for president? Ohio Gov. John Kasich joined the Republican field July 21 as he formally announced his White House bid.



"I am here to ask you for your prayers, for your support ... because I have decided to run for president of the United States," Kasich told his kickoff rally at the Ohio State University. Hide Caption 4 of 6 Photos: Who's running for president?



"Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hillary Clinton launched her presidential bid on April 12 through a video message on social media. The former first lady, senator and secretary of state is considered the front-runner among possible Democratic candidates."Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hide Caption 5 of 6 Photos: Who's running for president?



"This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Sen. Bernie Sanders , an independent from Vermont who caucuses with Democrats, announced his run in an email to supporters on April 30. He has said the United States needs a "political revolution" of working-class Americans to take back control of the government from billionaires."This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Hide Caption 6 of 6

Rubio, however, has picked up the pace of his fundraising off his strong debate performances. Many voters in early states like Nevada count him among their top contenders in interviews. His campaign is spending carefully to avoid running out of money.

In a memo to Bush supporters, campaign manager Danny Diaz said the fundraising number is "particularly noteworthy given the depth of the current field."

"We knew from the start this was going to be a hard fought and close race, but few could have anticipated just how volatile this field would be," he wrote.

And he emphasized that the campaign is playing the long game. "The overall effort supporting Jeb will be better funded than any other in the entire field and the campaign has a formidable grassroots organization in the early states that is making thousands of voter contacts and recruiting volunteers for February," Diaz wrote.

Brett Doster, Bush's strategic lead consultant for South Carolina, noted the campaign is expanding its operation in the Palmetto State as part of the long-term plan. "This is part of a bigger strategy," he said. "It's impossible for a presidential campaign to be successful long-term if they don't run a balanced campaign between air war versus ground game."

Doster added: "We have the resources we need to go deep into this primary process. "Nobody is going to have a headquarters in Columbia and three field offices this early in the campaign."