The Republican presidential field swelled Monday to nine candidates as South Carolina Sen. Lindsey Graham officially entered the 2016 race, making campaign fundraising even more challenging for those still on the sidelines. 

The list of potential candidates who have not yet announced includes: former Florida Gov. Jeb Bush, Wisconsin Gov. Scott Walker, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich, Texas Gov. Rick Perry and Louisiana Gov. Bobby Jindal.

Each of the hopefuls has a unique set of challenges, to be sure. But for those at the bottom of the polls, the ability to raise money likely becomes more difficult as more candidates enter the race. 

On Sunday, Kasich and Jindal each responded to questions about whether they had waited too long to enter, with Kasich alluding to the money factor.

“If I think I can't win, I wouldn't do it because I don't want to burden my family and my friends,” Kasich told NBC's "Meet the Press." “I raised money the old fashioned way. I go out and tell people what I think. … I'm optimistic where we are. I'm optimistic on the resources. I'm becoming more and more optimistic on the organization.”

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Jindal, who is polling near the bottom in the list of roughly 14 GOP candidates and hopefuls and plans to announce his intentions at the end of the month, said the race will “ultimately be up to the voters.”

“I think every politician says this is the most important election of our lifetime,” he told ABC's "This Week." “This really is.” 

Graham enters the race also running well behind in early polls but is running on a tough national security message and could use his home state's status as holder of the first-in-the-South primary to his advantage. 

But arguably bigger fish have yet to jump in the 2016 pool -- namely, heavyweights like Bush and Walker. Right now, they still enjoy solid numbers in the polls and have already lined up a fundraising network. 

David Payne, a Republicans strategist and partner at the Washington, D.C.-based firm Vox Global, voiced confidence in their ability to keep raising money, even on the sidelines. 

“There’s still time for serious contenders to ‘ante up,’” he said. “Our current campaign finance laws are making this one of the most interesting primary campaigns ever for Republicans, but also confusing. Two of our top-three contenders are running without officially declaring their candidacy as of yet: Bush and Walker.”

Political analysts have predicted Bush’s Rise to Rise super PAC will collect $100 million to $500 million by the July 15 federal filing deadline. It reportedly has done so well that Bush has asked donors to limit contributions to $1 million.

Walker certainly cannot match Bush’s extensive donor list, built with help from his father George H.W. Bush and brother George W. Bush’s presidential campaigns.

However, Walker has reportedly amassed a sizeable amount of cash through his political group, Our American Revival, pulling from small-dollar contributors and such mega-donors as casino magnate Sheldon Anderson and millionaire investor Foster Friess. The super PAC Unintimidated PAC is also raising money to help Walker.

The field of nine declared candidates is Graham, Sens. Ted Cruz, Rand Paul and Marco Rubio, former Arkansas Gov. Mike Huckabee, ex-Hewlett-Packard executive Carly Fiorina, former New York Gov. George Pataki, retired pediatric neurosurgeon Ben Carson and former Pennsylvania Sen. Rick Santorum.  

Still, fundraisers and analysts predict as much as $5 billion could be spent on the entire 2016 White House race, twice as much as in 2012, with Democratic frontrunner and fundraising juggernaut Hillary Clinton able to collect and spend as much as $1.5 billion.

“If … Christie or Kasich decide to get in the race, they would instantly command more attention and more money than most of the individuals who have already filed their official paperwork,” Payne said. “Late summer 2015 will clear up all this confusion about who’s actually running and who our top candidates are in the early primary states. ... 

"If you’re a candidate who’s still playing it coy in August, it will be too late for you.”