Former Florida governor Jeb Bush, left, is headlining $100,000-a-head fundraisers for a ballooning super PAC; the political committee for Wisconsin Gov. Scott Walker, right, is soliciting corporate money and six-figure checks. ((Bloomberg; AP))

In the last presidential contest, super PACs were an exotic add-on for most candidates. This time, they are the first priority.

Already, operatives with close ties to eight likely White House contenders have launched political committees that can accept unlimited donations — before any of them has even declared their candidacy. The latest, a super PAC called America Leads that plans to support Gov. Chris Christie of New Jersey, was announced Thursday.

The goal is simple: Potential candidates want to help their super PAC allies raise as much money as possible now, before their official campaigns start. That’s because once they announce their bids, federal rules require them to keep their distance.

Official candidates can still appear at super PAC fundraisers, but they cannot ask donors to give more than $5,000. And they cannot share inside strategic information with those running the group.

“Once someone becomes a candidate, there will be some very important guardrails you have to abide by,” said Michael E. Toner, a Republican campaign finance attorney who served on the Federal Election Commission.

But for now, there are few guardrails for most of the 2016 hopefuls. That’s why former Florida governor Jeb Bush is headlining $100,000-a-head fundraisers for a super PAC already ballooning with tens of millions of dollars in donations. Wisconsin Gov. Scott Walker’s political committee is soliciting corporate money and six-figure checks. And on Monday in New York, former New York governor George Pataki was the guest of honor at a fundraiser for his super PAC at a private Manhattan club, where co-chairs were asked to contribute $250,000 each.

The aggressive and open manner in which many White House hopefuls are embracing super PACs has startled many campaign finance experts, who say they are venturing onto untested legal ground even as undeclared candidates.

“We’re seeing a bending and an abuse and an evasion of federal campaign contribution limits to an extent that we’ve never before seen,” said Paul S. Ryan, senior counsel at the Campaign Legal Center, which seeks tougher campaign finance restrictions.

Candidates took pains to steer clear of their big-money allies in public during the past few election cycles, but there is little such distancing now.

Bush’s leadership committee and super PAC share the same name, Right to Rise, and were set up by the same GOP election law attorney, Charlie Spies. Walker’s Our American Revival political committee — registered under section 527 of the tax code, allowing it to collect unlimited donations like a super PAC — is being run by Rick Wiley, the veteran Republican strategist who is expected to helm his official campaign. We the People Not Washington, the super PAC backing Pataki, features his photo and bio prominently on its Web site, along with a form to request a meeting with him. And a new super PAC launched last week to back former Texas governor Rick Perry called the Opportunity and Freedom PAC is being run by Austin Barbour, brother of Perry adviser Henry Barbour.

In meetings with top political contributors, representatives of the presumptive candidates regularly lay out a menu of options that include making donations to a super PAC, according to multiple people familiar with the sessions. And unlike before, that no longer sets off alarm bells.

“It used to be that donors were very concerned that the super PAC was independent of the candidate,” said Robert Kelner, a Washington election law attorney. But now, he said, “candidates appear to be essentially establishing their own super PACs. In the absence of enforcement or even serious media scrutiny, donors will tend to conclude that they don’t have to worry.”

The presumptive Democratic front-runner, Hillary Rodham Clinton, is keeping her distance from a network of super PACs and advocacy groups that are gearing up to back her campaign.

But on the GOP side, presumptive candidates have been engaged in a frantic hunt for wealthy political patrons for their super PAC allies. During the past two months, their schedules have been packed with visits to the Manhattan offices of billionaire hedge-fund managers and appearances at private donor conferences, such as a January event in Rancho Mirage, Calif., for backers of a political network organized by the industrialists Charles and David Koch.

“It really is a charade that we have any semblance of campaign finance limits,” said Miles Rapoport, president of Common Cause, which seeks to lessen the influence of money on politics. “What we’re seeing is a wealth primary to the tenth degree, where what candidates are doing is chasing a very small number of people who can make or break their candidacies from day one.”

Even some of those writing the big checks are uncomfortable with the new order.

“I do not like the super PACs,” said Chicago private-equity executive Bill Kunkler. “I think it’s the lowest return on investment.”

Nevertheless, Kunkler recently donated $25,000 to Bush’s super PAC. “I want to support the presumptive candidate, and that’s the vehicle,” Kunkler explained, adding: “We have got to reform how our political system is being financed. It’s just crazy.”

Campaign finance lawyers said the close ties between the likely candidates and their super-PAC allies pose serious legal questions, including whether the groups could later be considered affiliated with the eventual campaign or viewed as an entity created by the candidate. That could limit their ability to spend money raised outside candidate contribution limits, which stand at $2,700 per person for the 2016 primaries.

There’s little chance, however, that such issues will be wrestled with at a sharply divided Federal Election Commission, which hasdeadlocked over whether to even open up enforcement investigations.

The intense super PAC fundraising is also viewed by some critics as evidence that the presumptive candidates are “testing the waters,” a legal term used by the FEC to refer to activities undertaken by a possible candidate, such as polling and traveling to key states to measure support for a bid. Such activities can only be paid for by money raised under the candidate contribution limit, but they do not have to be reported to the FEC unless the person testing the waters decides to become a candidate.

So far, only three contenders — Sen. Lindsey O. Graham (R-S.C.), former senator Jim Webb (D-Va.) and retired Maryland neurosurgeon Ben Carson (R) — have announced that they are testing the waters and have set up political committees to raise funds for that purpose.

Bush spokeswoman Kristy Campbell said that his team is “fully complying with the law in all activities that Governor Bush is engaging in on the political front.”

“If Governor Bush engages in any testing-the-waters activities, they will be paid for appropriately under the law and reported at the required time,” she added.

One category of 2016 contenders cannot take part in the early super PAC rush: federal officeholders, who, like official candidates, can’t coordinate with the groups. That’s one reason there are no major super PACs yet for GOP Sens. Marco Rubio of Florida, Rand Paul of Kentucky and Ted Cruz of Texas, all of whom are considering presidential bids.

After the campaigns officially kick off, candidate-specific super PACs are poised to be central to the 2016 race. The big-money groups are likely to fuel a protracted fight for the Republican nomination — a more intense version of what happened in 2012, when wealthy backers financed super PACs that helped former House speaker Newt Gingrich and former senator Rick Santorum of Pennsylvania wound former Massachusetts governor Mitt Romney.

This time around, GOP strategists believe that at least half a dozen candidates could be flanked by super PACs sitting on millions as they head into the Iowa caucuses, including Bush, Christie, Cruz, Paul, Rubio and Walker.

“They could change the way we’ve always looked at the process for the nomination,” said Ron Weiser, a former finance chairman of the Republican National Committee, noting that candidates who do well in the early primaries usually enjoy a rush of donations. “But what’s that mean when other candidates’ super PACs have amounts substantially in excess of that?”

It remains to be seen how the White House contenders will handle their big-money allies once they have no direct control over the groups.

Asked by reporters in Iowa on Saturday whether he would call on his aligned super PAC to refrain from running negative ads, Bush said, “My hope is that we’ll have a positive campaign. It’s possible a super PAC could be a positive message, as well.”

He brushed off the question when asked again: “That’s way in the future.”

Ed O’Keefe and Philip Rucker in Cedar Rapids, Iowa, contributed to this report.