This week, Mitt Romney disclosed the identities of people who have donated to him over the past three months, and while many of his biggest contributors work at top financial firms such as Goldman Sachs and Morgan Stanley, those companies are not his largest source.

That is a much more surprising — and modest — company: the Rothman Institute, a Philadelphia-based orthopedic clinic. Sixty-five doctors at the chain, which comprises more than 15 offices, donated to Romney on Sept. 17, including 20 who each gave $25,000, according to the report filed with the Federal Election Commission. The money went to Romney Victory, a joint effort of Romney’s campaign and the Republican Party, which will spend on his behalf. An executive with the company did not return a call requesting comment.

The contributions from Rothman doctors add up to $751,000, which is over 50 percent more than the next highest total, $480,000, donated by employees of the private equity firm Kohlberg Kravis Roberts. The companies themselves cannot donate, but employees and top executives make the contributions with their own money, often with their business interests in mind.

Financial firms such as KKR and energy giant Occidental Petroleum fill out the rest of Romney’s top sources of money. Romney also raised $266,000 from executives at NASCAR. Romney said earlier this year that he doesn’t follow the sport very closely, but he added, “I have some great friends who are NASCAR team owners.”

Another top source was the education software company Jenzabar, which is run by Massachusetts Republican Party Chairman Robert Maginn, a top Romney supporter. A former executive sued Jenzabar and Maginn in the summer, alleging, among other things, that the company reimbursed employees for their donations, according to a report in the Boston Globe.

Jenzabar employees gave $165,000 to Romney during the third quarter, and the company itself donated $250,000 to Restore Our Future, a super PAC backingRomney. A company official did not return a call requesting comment.

The disclosures show that three lobbyists raised about $1 million each for Romney Victory over the past three months: David Beightol, of Dutko Grayling; Bill Graves, at the American Trucking Associations; and Dirk Van Dongen, at the National Association of Wholesaler-Distributors. A Romney campaign spokeswoman declined to comment.

Around the country

Massachusetts Senate candidate Elizabeth Warren, the Democratic challenger to Sen. Scott Brown (R), had one of the biggest fundraising quarters on record, raising $12.1 million from June to September. Warren’s sum, surpassed by only a handful of candidates in history, is considerably more than the $7.5 million raised by Brown.

Around the country, a surprising number of challengers outraised their incumbent opponents, including almost two dozen in the House, representing both parties.

Iraq veteran Tammy Duckworth, challenging Rep. Joe Walsh (R-Ill.), raised $1.5 million, about the same figure as House Speaker John A. Boehner (R-Ohio). Conservative Mia Love of Utah raised twice as much as Rep. Jim Matheson (D), bringing in $1 million to Matheson’s $471,000, according to reports. Both Duckworth and Love had prominent speaking roles at their party conventions this year.

Rep. Allen B. West (R-Fla.), a favorite of tea party members, raised $4.9 million, more than any other House candidate, including $2.4 million from donors giving less than $200. West also has benefited from spending by the Treasure Coast Jobs Coalition, funded by a $1 million donation from Richard Roberts, a New Jersey pharmaceutical executive.

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