Marco Rubio's highly touted debate performance on Wednesday has already yielded a significant tangible benefit: The Republican presidential candidate has snagged the support of mega-donor Paul Singer, in a move that will be widely seen in the political world as a blow to struggling rival Jeb Bush.

One of the party's most prolific and hard-to-please donors, Singer gave more than $16 million to candidates and political committees in the last four years, according to records on file with the Federal Election Commission. Fiscally conservative and socially moderate, the hedge-fund manager has donated to conservative candidates and causes, such as pro-Israel groups, former Ambassador John Bolton, and the Tea Party Patriots, but he has steered many of his contributions to his own super political action committee, American Unity, which supports Republicans who back gay rights. He gave $1 million to Restore Our Future, the super-PAC supporting Mitt Romney's 2012 presidential campaign, and he supported former New York City Mayor Rudy Giuliani's 2008 White House bid.

Over the last two presidential cycles Singer, founder of Elliott Management, convened private meetings of his fellow wealthy New York Republicans, at which presidential candidates effectively audition for support. A Harvard law school graduate, Singer started his firm in 1977 with $1.3 million that friends and family staked him. The New York-based firm now oversees assets valued at more than $25 billion. Its flagship fund has lost money in just two calendar years.

There is a strong possibility that Singer's endorsement will send a signal to other undecided bundlers to cast their lot with Rubio. Such is Singer's influence in the donor community that it is conceivable that his move will cause some current backers of Bush to jump ship. That potential dynamic has been watched for closely since Wednesday's debate, although Rubio's advisers have cautioned not to expect an immediate wave of defections. Among the currently unaffiliated mega-donors who could be influenced by Singer's choice are industrialist David Koch; Philip Anschutz, a Denver-based oilman and entertainment entrepreneur; Charles Schwab, founder of the eponymous brokerage firm; and Chicago Cubs owner Todd Ricketts. All are part of Singer's network. Ricketts was a national finance chairman for Wisconsin Governor Scott Walker, who dropped out of the presidential race in September.

Singer already is preparing to exercise his influence on Rubio's behalf. In an e-mailed letter he began sending to members of his circle on Friday afternoon, many of whom have given in the past to Republican presidential candidates but have remained uncommitted so far in this cycle, Singer asks them to join him in backing Rubio, whom he praises for his “vision” and his ability to deliver “a compelling argument for using conservative ideas to help America adapt and thrive in the 21st century.”

“In a field full of promise, but also of risk for the party, Senator Rubio is the strongest choice,” Singer wrote, noting the Florida senator's “substantive views well suited to both the primary and general electorate.”

After a debate performance in which his attempt to attack Rubio, a one-time political protege, backfired, Bush and his top campaign aides held a conference call with donors this week in an attempt to reassure them. For Singer, however, the debate was decisive. According to a person familiar with his thinking, the billionaire investor had been leaning toward Rubio for some time, and the Bush campaign, knowing that, tried to head him off. In a signal of how influential Singer can be, representatives for Bush in the finance community had pleaded that he hold off on making a decision—to give Bush more time. But after what he saw on the debate stage Wednesday, Singer did not believe he would learn more that would influence his decision, according to a source familiar with his thinking. He did not believe Bush could beat front-runner Donald Trump, or fend off a possible surge by ultra-conservative U.S. Senator Ted Cruz, or that the son and brother of two previous presidents could beat former Secretary of State Hillary Clinton, the Democratic front-runner. Singer wants to consolidate support behind someone he believes can accomplish all of those tasks.

“It's my highest priority to support the candidate for president who can...navigate this complex primary process, and still be in a position to defeat Secretary Clinton in November 2016,” Singer wrote in the letter.

Singer eventually will provide super-PAC money on Rubio's behalf but for the short-term plans to focus on bundling—collecting money from his wide network of political donors—for Rubio's official campaign committee between now and the start of the caucuses and primaries in early February.

Before it's here, it's on the Bloomberg Terminal. LEARN MORE