But among the 2012 GOP candidates, Newt Gingrich owes the most, hands down. He owed $4.9 million as of his last disclosure Sept. 30, but after renting his list of supporters and reaching agreements with creditors, he'll close the year owing $4.6 million, spokesman R.C. Hammond said.
"Repayment doesn't come overnight," Hammond told ABC, calling it a "steady effort" and noting that after Republicans' loss in 2012, reviving donors' interest will take time. "It will be over a matter of years that the debt will be paid down."
As he campaigned in Florida against a well-funded Romney machine, with victory in sight after a win in South Carolina, Gingrich's campaign exhausted its financial resources while fighting back against Romney's barrage of attack ads.
"You know, Romney spent $20 million in Florida in three weeks, and I think some of our guys decided to try to match him," Gingrich told ABC News in April.
His list of 130 creditors in 31 states is long and tangled. As of his last FEC filing, Gingrich owed rent in at least two states, and utilities in at least three. He owed the South Carolina GOP $4,400 for lodging. He owed more than $440,000 to his private-security company, Patriot Group of Warrenton, Va.
He still had not paid Moby Dick Airways for more than $1 million in air-travel costs. He owed former primary competitor Herman Cain Solutions more than $16,500 for "strategic consulting-travel." He owed JC Watts Enterprises for consulting.
He owed a $10,000 insurance deductable to a firm in Atlanta. He owed Twitter $12,763 for a "media buy." He owed "ballot access fees" to firms or individuals in three states, including $4,000 in Virginia, where he did not appear on the ballot. He is disputing $217,500 in software licensing fees from three companies, and another $6,537 in travel costs to one individual. And he owes himself $647,518 for travel.
Two of his creditors, both small businesses that spoke with ABC News about Gingrich's debts in May, say they're still frustrated with the unpaid bills.
"It's very disappointing that you do the work for them and you meet their deadlines and jump through all their hoops, and this happens," Vic Buttermore of Signs Unlimited SEA in Ocala, Fla., told ABC News in a recent phone interview.
Gingrich still owes him more than $13,000 for printing and shipping "Newt 2012" lawn signs to a handful of states. Buttermore says he has ended up printing the signs at "a big loss" after costs including shipping.
"Every time we called up there someone else was new and they were checking on it," Buttermore said.
Event setup company Pro Production Services of Phoenix, Ariz., doubts whether it will be paid more than $35,000 for a handful of Gingrich events in Nevada before the Feb. 4 caucuses.
"I don't think anybody, when you're running a business, is happy to get stiffed on any amount of money," Ryan Driscoll, a project manager for Pro Production Services, said.
Driscoll said most of the debt was cost-fronted by Pro Production.
"The debt that he owes us includes our labor, transport, lodging, and then also the equipment rental," Driscoll said. "That's why it was such a big deal to begin with for us; that's a lot of money to just float out there."
Not all Gingrich's creditors are so mad, and several declined to comment on the debts he owes them. For consultants, media buyers and others in the campaign industry, delayed payment goes with the territory.
Another class of creditor, meanwhile, will turn a profit on the 2012 campaign: banks. The parties each took out multimillion-dollar loans and, according to his last disclosure, Romney's campaign still owed $3 million of a $20 million loan from Bank of Georgetown, which will reap the benefits of a 4.5 percent interest rate.