Bernie Sanders is no friend to big business, but at least one industry has profited thanks to his candidacy. A Washington Post analysis of federal campaign finance disclosures published Thursday found that the Democratic presidential hopeful is the biggest spender of any candidate this year, with the bulk of his campaign's expenditures going to political consultants.

Several consulting firms have reaped millions from the Sanders campaign, most notably the media agency Old Towne Media and Revolution Messaging, a consulting firm led by veterans of Barack Obama's 2008 presidential campaign. Old Towne Media has received nearly $25 million from the Sanders campaign and Revolution Messaging has collected more than $16 million, according to the Center for Responsive Politics.

The size of these expenditures highlights just how important the political consulting business has become to the modern campaign cycle. While Sanders has managed to generate a staggering amount of campaign money without depending on large donors or traditional fundraising techniques, he has maintained a conventional reliance on consulting firms.

John Hopkins University political scientist Adam Sheingate, the author of "Building a Business of Politics: The Rise of Political Consulting and the Transformation of American Democracy," has tracked the growth of the political consulting industry in-depth. Sheingate told International Business Times he wasn't surprised by the large role of consultants in the Sanders campaign.

"Generally speaking, if you look at every campaign, they generally have one or two main firms that are handling the bulk of their expenses," said Sheingate. "They also tend to be associated with advisers in the inner circle."

Old Towne Media is linked to Tad Devine, a senior strategist for the Sanders campaign and a frequent surrogate. One of the partners in Revolution Messaging, Tim Tagaris, is widely credited with building the Sanders campaign's innovative fundraising apparatus.

Democratic front-runner Hillary Clinton, meanwhile, has spent nearly $22 million on services from the firm GMMB, where her close adviser Jim Margolis is a senior partner, according to data from the Center for Responsive Politics. The Benenson Strategy Group, led by chief Clinton strategist Joel Benenson, has received almost $2 million from the campaign.

Sheingate told IBT that while he doesn't have anything against political consulting, he does think the structure of the industry can bias campaigns toward certain strategies. Consulting firms often earn a share of a campaign's spending on things like ad buys, which gives consultants a financial incentive to urge greater media spending — independent of its efficacy.

"The folk wisdom is you've got to buy ads to be successful. That's how consultants think the political system works," said Sheingate. "And there's research that suggests that ads are not as effective as the amount of money they spend on them indicates."

That said, Sheingate credited the Sanders campaign's fundraising juggernaut to the help of consultants. "It's driven by the grassroots, but it also requires this highly professionalized infrastructure to work effectively," he said.

Sunlight Foundation policy analyst Richard Skinner said the consulting firms act as connective tissue between candidates and the larger political party infrastructure.

"Not only are they adding skills that the campaigns need, but they're a signal to potential contributors, to potential endorsers, to groups of all kinds, that you're running a serious campaign," said Skinner. "Also, consultants are able to access personal ties to other consultants, to groups, to party committees."

RTX2BX9Z Supporters cheer as U.S. Democratic presidential candidate Bernie Sanders (I-VT) speaks at a campaign event at Purdue University in West Lafayette, Indiana, April 27, 2016. Photo: REUTERS/Aaron P. Bernstein

One leading candidate has managed to do without those services, for the most part. Instead of pouring millions into ads, Republican front-runner Donald Trump has centered his campaign strategy around efforts to attract free media, with a great deal of success. His biggest expenditure, according to the Center for Responsive Politics, has been $7.5 million Rick Reed Media, which is headed up by longtime Republican operative Rick Reed.

But Trump may be an exceptional case, not to be replicated any time soon. The bombastic businessman came into the campaign with exceedingly high name recognition, and has been able to garner far more free media than any other candidate, at a much lower cost.

Still, Sheingate predicted that Republican consulting firms would be able to cash in on Trump eventually, assuming he wins the nomination. Once the entire party is aligned behind him as their chosen candidate, the party and its affiliated firms will be invested in his success.

"There will be ads in support of Trump because people will rally behind him," said Sheingate. "Those ads will be handled by the industry."