His latest book, "One Nation," outsold Hillary Clinton’s memoir. Yet Ben Carson still remains one of the lesser-known Republican presidential candidates, with the fundraising prospects of a severe underdog.

Carson is a renowned pediatric neurosurgeon who has never run for office before. But he became a Tea Party favorite in recent years due to relentless criticism of the Affordable Care Act, President Obama’s signature health-reform law, plus a yearlong stint as a Fox News commentator and speaking appearances around the country before conservative and libertarian groups.

Carson’s personal narrative is the stuff campaign managers drool over. He and his two brothers were raised in Detroit by an illiterate single mother who worked dawn to dusk to pay the rent. Yet Carson made it to Yale and the University of Michigan Medical School, and became head of pediatric neurology at Johns Hopkins University at age 33. With his candidacy now official, Carson will test whether he can transform the popularity of a Tea Party hero into a campaign war chest and, ultimately, votes.

In 2013, the year Carson retired from Johns Hopkins, supporters led by John Philip Sousa IV, great-grandson of the famous composer, formed a super PAC called the National Draft Ben Carson for President Committee, to raise money for a Carson presidential run. That group surprised political analysts by pulling in $13.5 million in 2014—more than a similar super PAC for Hillary Clinton, which raised just $12.9 million.

Carson stumbled this year, telling CNN that he knows homosexuality is a choice because criminals "go into prison straight -- and when they come out, they're gay." A ruckus ensued and Carson quickly apologized. There are now at least three other political action groups affiliated with Carson—USA First, One Nation and American Legacy—and they've raised far less than the Draft Carson group. But they’ll likely serve as fundraising vehicles for Carson and causes he supports, now that he’s officially running. Here are the donors who gave the most to the Draft Carson super PAC in 2014:

Mark Oldfield, owner and CEO of Source Support Services, a Georgia IT firm. Oldfield shares the No. 1 spot as top donor to the Draft Carson super PAC in 2014, giving $101,520.

Mike Horan, president of Ajax Paving Industries, a concrete and asphalt firm with offices in Michigan and Florida. Horan also donated $101,520.

Harry Bettis, an Idaho rancher who supports Republican candidates and causes. Donation: at least $71,000, which appears to be his largest contribution to any candidate.

Caster Family Trust, a family operation in San Diego linked with Terence Caster, who owns A-1 Self Storage, a chain that has been boycotted because Caster helped fund efforts to ban gay marriage in California. Donation to Carson: at least $50,000.

Jeanette Quilhot, co-owner of an Indiana horse farm. Donation: at least $80,000.

Carson’s donor list is considerably different from those of most major candidates, who typically claim Wall Street billionaires, big-name CEOs, law-firm partners and other wealthy insiders as their top sources of money. Clinton, for instance, has rich friends in dozens of industries, which is why she’s considered a fundraising dynamo. Since Carson has never been in government, he’s never developed the sort of relationships with moneyed interests that senators, governors, secretaries of state and first ladies do. The vast majority of his funding comes not from wealthy activists but from political unknowns contributing less than $1,000.

Still, Carson’s appeal will have to extend beyond self-made entrepreneurs and rugged individualists if he hopes to become anything more than a fringe candidate. The winning candidate in 2016 may have to raise nearly $1 billion to fund the ads, outreach and voter education needed to attain the White House. It would take hundreds of bestsellers to match that, no matter how great the story.

Rick Newman’s latest book is Liberty for All: A Manifesto for Reclaiming Financial and Political Freedom. Follow him on Twitter: @rickjnewman.

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