Billionaire casino mogul Sheldon Adelson, which wife Miriam Adelson, is one of the GOP’s biggest contributors. (Chip Somodevilla/Getty Images)

The 2016 Republican presidential contest, designed to be a tidy affair, is instead shaping up to be a chaotic, drawn-out slog, thanks largely to an expanding pool of rich patrons raining money on a broad field of candidates.

Former Florida governor Jeb Bush has raised tens of millions of dollars for his allied super PAC, collecting a historic amount, he told donors Sunday night. But that hasn’t been enough to stop his rivals from amassing their own stockpiles. A super PAC supporting Sen. Marco Rubio of Florida secured about $20 million in commitments in less than two weeks, according to people familiar with the totals. An independent operation backing Sen. Ted Cruz of Texas says it pulled in $31 million in a single week. A new super PAC allied with Wisconsin Gov. Scott Walker has almost matched that in pledges, fundraisers say.

Never have so many candidates entered a White House contest boosted by such huge sums. The financial arms race could fuel a protracted primary season similar to the one in 2012 — exactly what party leaders were hoping to avoid.

“There could be as many as a dozen candidates that have a threshold amount of money in their campaigns and super PACs to compete vigorously in the early states,” said Phil Cox, a Republican strategist who runs America Leads, a super PAC supporting New Jersey Gov. Chris Christie that has the backing of at least two billionaires.

Some party operatives say 2016 could be the first race in the modern era in which a candidate does not need to win Iowa or New Hampshire to prevail. Strong showings in those early states have historically translated into much-needed financial momentum. But this time, wealthy patrons might keep their favorite picks aloft through independent spending.

David Koch. (Travis Heying/AP)

Contenders such as Cruz and former Arkansas governor Mike Huckabee are crafting long-game strategies, staking their hopes on a wave of Southern-state primaries that will not take place until March. Although next year’s compressed primary schedule could intensify the momentum for a front-runner, it could also help a range of contenders pick up delegates if a single leader does not emerge quickly.

The political money boom is being driven largely by super PACs, which can collect unlimited donations from individuals and corporations. The groups are supposed to operate independently from the candidates they support, but in this race they are functioning as de facto arms of the campaigns.

Fifteen White House contenders are being boosted by big-money groups run by their close allies. Most have not yet declared their candidacies but are instead hopscotching the country headlining high-dollar super-PAC fundraisers.

By blessing the groups, the aspirants have given a green light to supporters once wary of such outfits.

“There’s no question that donors are much more comfortable with super PACs,” said Austin Barbour, a Mississippi-based strategist who is running the Opportunity and Freedom PAC, which is backing former Texas governor Rick Perry. “These guys who are worth $100 million or a billion dollars now say, ‘I understand this super-PAC stuff.’ They see that the potential candidates or candidates have a ton of trust and faith in them.”

There’s also been an influx of new contributors and bundlers, GOP fundraisers say. They include executives in the financial-services and oil and gas industries who are upset about federal regulations, as well as conservative Jews alarmed by President Obama’s fraught relationship with Israeli Prime Minister Benjamin Netanyahu.

The 2016 contenders and their big-money backers

Much of the establishment money is flowing to Bush, who senior Republicans predict will collect $100 million for his super PAC by the end of May.

But his competitors have their own wealthy benefactors. Rubio is being backed by Florida billionaire Norman Braman, who has committed $10 million to his aligned super PAC. Cruz is getting support from the family of hedge-fund tycoon Robert Mercer.

An influential network of conservative donors organized by industrialists Charles and David Koch is touting the merits of five contenders: Bush, Walker, Rubio, Cruz and Sen. Rand Paul of Kentucky. It also remains to be seen who will win the support of billionaire casino mogul Sheldon Adelson, one of the party’s biggest contributors.

Money could actually be less of a determining factor than it has been in the past, some party strategists said. When Bush finally rolls out his eye-popping total, it will be unlikely to have the impact that his brother George W. Bush’s then-record haul of $37 million did in mid-1999.

Jeb Bush has conceded that his gold-plated political name isn’t deterring most opponents.

“I don’t see any coronation coming my way, trust me,” he told a skeptical GOP voter last weekend in New Hampshire. “I’m really intimidating a whole bunch of folks, aren’t I?”

The competitive money race was one of the big topics Sunday as Bush and his team hosted 350 top donors and fundraisers at a swanky Miami Beach hotel.

The donor confab, which concluded Monday, was led by Bush’s top three aides: David Kochel and Sally Bradshaw, who are expected to lead his campaign, and Mike Murphy, who is poised to lead the super PAC. The briefings included discussions of economic and foreign policy and details on how the super PAC, Right to Rise, plans to reach out to “non-traditional GOP communities.”

But some attendees were also eager to hear how Bush will fend off rising competitors such as Rubio, who has cast himself as the face of the party’s future.

“Marco is so much better communicating and makes the generational point without saying a word,” said one big contributor who is supporting Bush and spoke on the condition of anonymity to describe private conversations. “Basically the fear is really about Rubio gaining traction with donors. With money, he is the real problem for Jeb.”

The 2016 primary contest could resemble the fracas in 2012, when super-PAC benefactors kept alive the bids of former House speaker Newt Gingrich and former U.S. senator Rick Santorum of Pennsylvania, forcing Mitt Romney into an extended fight for the nomination.

Adelson and his family poured $15 million into a super PAC backing Gingrich, then an unthinkably large amount. This time, with more big spenders in the mix, such sums could be commonplace, the former House speaker said.

“What seems like really big money is less than a yacht,” Gingrich said in an interview. Wealthy donors could decide that “this year, instead of buying a new yacht, I’m going to spend $70 million on a candidate,” he said.

Hoping to avoid a replay of 2012, the Republican National Committee has curtailed the number of debates and compressed the primary season. “There will be a historical number of folks in the mix, but we will still have a nominee sooner,” RNC spokesman Sean Spicer said.

Party officials, however, are still struggling to figure out what criteria to use to decide who will get to participate in the official debates. “It’s a work in progress,” Spicer said.

By the time the first debate is held in Cleveland in August, there is likely to be nearly a dozen declared candidates, if not more.

The party has also sought to speed up the nomination process by pushing back the Iowa caucuses and moving up the convention to July. The first four contests are on track to be held in February, followed by more than a half-dozen states in early March, including heavyweights such as Texas.

There could be a full roster of candidates still competing by then, lifted by well-funded outside allies. Some could try to cherry-pick states where they have an advantage, winning delegates that they carry to the convention, said Rick Hohlt, a Washington lobbyist and longtime party fundraiser. “It’s become entirely unpredictable,” he said.

Candidates will be able to lean more heavily on big-money groups, which are expanding beyond just television ads.

The Bush-aligned Right to Rise is planning to invest heavily in not just paid media but also a sophisticated digital voter outreach effort, according to people familiar with the plan. A nonprofit group run by a Bush ally is set to serve as an outside policy shop.

When asked about the state of campaign finance laws before his big donor meeting on Sunday, Bush said: “They are what they are. Campaigns are going to have to play within those rules.

“I don’t think you need to spend $1 billion to be elected president of the United States in 2016,” he told reporters, adding, “But in order to be competitive, you’ve got to raise a significant sum of money to build a first-rate policy team and a great campaign.”

The extra freight carried by super PACs could help candidates broaden their operations beyond the states that hold the first few contests early in the race.

Cruz’s campaign, which has raised $6 million since he announced in late March, is building a low-cost national infrastructure. His advisers have assessed which states offer the chance to pick up the most delegates and have assigned a dollar value to the most efficient media markets.

Because the official campaigns can raise only $2,700 per individual, some super-PAC budgets could end up outstripping those of their candidates.

“It would not surprise me to have America Leads spend more on media and paid voter contact than the official Christie campaign, and I think you will see that with other campaigns, as well,” Cox said of his group.

For all the cover that wealthy benefactors will provide in 2016, however, party operatives said they won’t be able to pick the winner.

“Voters are still going to see who is viable, who is credible and who is not,” Barbour said. “But it does give you a puncher’s chance.”

Tom Hamburger, Sean Sullivan, Karen Tumulty and Katie Zezima contributed to this report.