Despite a wealth of choices in a crowded primary field, the vast majority of high-level Republican donors and fund-raisers have not yet backed any candidate financially, magnifying the importance of the coming debates as the presidential hopefuls seek to impress potential backers.  Only about a fifth of the 1,000 or so fund-raisers and their spouses who rallied around Mitt Romney, the Republican nominee in 2012, have given money to any of the 2016 candidates, according to a New York Times review of fund-raising records reported by the candidates last week.  Those who remain uncommitted — hundreds of volunteer “bundlers” who could collect contributions from their friends and business associates — represent a huge pool of untapped campaign cash, potentially hundreds of millions of dollars, that could remake the primary campaign.  Some of the bundlers and donors said they had held back, in part, because the field was the strongest they had seen in years, with several viable contenders representing the party’s different generational and ideological segments.  Unlike in 2012, when Mr. Romney dominated fund-raising even as he fought off a series of insurgencies by more populist candidates, the affections of many donors in 2016 are divided among three or four candidates. Others are quietly weighing the impact of Donald J. Trump, who has jumped to the lead in some national polls despite raising almost no money from the party’s establishment.  “I haven’t committed to anyone at this point, and I’m not on the verge of committing to anyone,” said Paul E. Singer, a hedge fund manager who is among the most sought-after Republican bundlers in the country, at an investment conference last week. “I think there are a number of candidates that are smart, solid, good potential leaders, leaders and potential leaders.”  The slow recruitment of major donors and bundlers is also a function, several donors and Republican leaders said, of the candidates’ early emphasis on raising money for “super PACs,” which tend to be funded by a much smaller pool of extremely wealthy donors.  About 200 of the 1,000 people who bundled donations for the Republican candidate Mitt Romney in 2012 have made campaign contributions so far to 2016 candidates, including two Democrats.  Approximate number of Romney bundlers who have given to each candidate  Candidates cannot solicit the unlimited checks that fuel super PACs, and several White House aspirants delayed entering the race this year and spent the winter and spring securing commitments from mega-donors. One result: Vast amounts of money are already flowing into the Republican race, but mostly to super PACs, not candidates. Super PACs and outside groups backing individual Republican candidates have raised about $230 million, while the candidates took in just $64 million through the end of June.  “The super PAC donors were more important, to some extent eclipsing the traditional world of hundreds of bundlers,” said Fred Malek, the finance chairman of the Republican Governors Association. “The next quarter is going to be hugely different.”  Mr. Romney’s financial operation raised $1 billion in 2012, more than any Republican campaign in history, by combining those who raised money for former President George W. Bush with hundreds of new Republican bundlers, many of them from Wall Street. Some of Mr. Romney’s top bundlers, including the Oklahoma energy executive Harold Hamm and Joseph W. Craft, the chief executive of one of the country’s largest coal producers, have not yet given to a Republican candidate in 2016.  The Times analyzed a list of Mr. Romney’s bundlers and their spouses that USA Today assembled in 2012 with data from the Sunlight Foundation, which tracks invitations to political fund-raisers, and the Federal Election Commission, which requires that candidates disclose the names of registered lobbyists who raise money for them.  Jeb Bush, the former president’s brother, appears to have won over the largest share of Mr. Romney’s bundlers, with at least 120 donating to his campaign. They include Brian Ballard, a Florida lobbyist, and Dan Loeb, a hedge fund manager who shares Mr. Bush’s passion for education issues.  “Jeb’s record as a champion of parent choice and academic excellence is unparalleled,” Mr. Loeb said in an email. “He understands that as a nation we have a responsibility to even the playing field through education so that every child has a chance at the American dream.”  Some bundlers are committed to Republicans who did not enter the race until July and have not yet reported any fund-raising numbers, such as Gov. Scott Walker of Wisconsin. An unknown number may have given to the candidates’ super PACs, which do not have to report their donors until the end of July.  Other bundlers, like Jenny Craig, the California-based diet guru, have given to multiple candidates. Still others, like Frank VanderSloot, who runs an Idaho-based health products company, are weighing the prospects of two candidates they like.  “Frank VanderSloot is committed to helping both Marco Rubio and Scott Walker get their messages out,” said Tony Lima, a spokesman for Mr. VanderSloot. “He is engaged in that process.”  But the scramble for other major bundlers is a boon for candidates not named Bush, several of whom are banking on the debates, which begin Aug. 6, as a chance to prove their mettle and recruit new donors and fund-raisers.  Almost 50 Romney bundlers, among them Wayne Berman, an executive at the Blackstone Group, and Harlan Crow, a Texas builder, have already given money to Mr. Rubio, the Florida senator; 14 each have contributed to Senators Ted Cruz of Texas and Lindsey Graham of South Carolina; and at least 10, including the prominent New York hedge fund manager John Paulson, have donated to Carly Fiorina, the former chief executive of Hewlett-Packard.  A separate analysis, looking at the top 250 donors to Republican candidates and party organizations, showed a similar phenomenon: Fewer than 100 have contributed to any of the 2016 candidates, according to the Times analysis. Some of them have contributed to more than one candidate, indicating that they are hedging their bets in what is likely to be a volatile and fiercely fought campaign.  “I decided to give all of the ones I like the support, just in case they made the primary,” said Elloine M. Clark, a Texas philanthropist who wrote large checks to Mr. Cruz, Mr. Rubio, Senator Rand Paul of Kentucky and Gov. Bobby Jindal of Louisiana.  “I didn’t want to cut anybody out,” Ms. Clark added. “I want to see some intelligent young people in the race.”  The Republican contenders are moving aggressively to tap that money. In recent weeks, some have begun shifting from raising money for their super PACs, which typically depend on a handful of ultra-wealthy donors, to their campaigns, which require the help of hundreds of bundlers and thousands of donors.  “As we talk to bundlers around the country, there is still a great pause going on right now,” said Ray Washburne, the finance chairman for Gov. Chris Christie of New Jersey. “There’s been no breakaway candidate, and everyone is waiting to see the first debate.”
With the first debates coming, many of the wealthiest Republican supporters have held off backing one candidate in a big 2016 field. Super PACs have also changed the giving calendar.