Jane Mayer focused national attention on such groups in an encyclopedic article about the Koch brothers last summer in The New Yorker. The article described how the Kochs had funded groups to promote their conservative political philosophy and oppose “so many Obama Administration policies—from heath-care reform to the economic-stimulus program—that, in political circles, their ideological network is known as the Kochtopus.”

Mayer said one of the most difficult tasks in reporting the story was finding the connections between the groups and their funders. Many people and organizations besides the Kochs fund advocacy groups, and from both ends of the political spectrum. Mayer said it takes so much effort to find out what group is connected with what organization that it is difficult for reporters to keep up.

“You never know what you don’t know—it is getting harder and harder to find out who is behind those front groups,” she said. That is no accident, according to Wendell Potter, a former vice president for corporate communications at CIGNA, the insurance company.

Potter, who has since become a vocal critic of corporate public relations, particularly related to the health-care debate, said PR’s influence has become deliberately more opaque as viewers become more attuned to its influence. During the debate over the Clinton health-care plan in 1993 and 1994, Potter said, the health-insurance industry’s trade group openly opposed the measure. In a series of ads featuring Harry and Louise, the fictional married couple, the industry warned that the Clinton plan would mire health care in tangled bureaucracy. The industry’s role in the ad, he said, “was very visible, very vocal.”

The industry’s opposition to the bill reflected the public’s concern at the time about government interference in health care, Potter said. But by 2007, public opinion had changed and polls showed that a majority of Americans felt that some degree of government involvement was needed.

Thus, Potter said, the industry no longer wanted to be closely linked to lobbying on the issue. So instead of directly running ads, it farmed a lot of the work out, obscuring its role.

“You really want someone that seems to be an ordinary person. That gives you credibility and the perception that the public is on your side,” he said.

The health-insurance industry’s trade group, America’s Health Insurance Plans or AHIP, declined to speak for this story. But executives with the public relations firm APCO Worldwide, which has worked for the health-care industry, said that when their agency sets up a group to fight for an issue, they don’t try to hide their association. B. Jay Cooper, APCO’s managing director, said in the recent health-care fight APCO managed such a group, but every reporter who covered the issue knew who APCO represented. That doesn’t mean the link was always reported to the public.

Indeed, it is often difficult for reporters to find the connection. It took Drew Armstrong, a health-care reporter for Bloomberg, months to nail stories showing how the health-insurance industry had funded efforts by the US Chamber of Commerce to fight against changing the health system.

Armstrong dug into tax records to show what had previously been hidden—that AHIP contributed a whopping $86.2 million to the Chamber to fight against the Obama health- care plan. “I was shocked by the amount,” Armstrong said. “It was 40 percent of the Chamber’s budget.”

The problem for Armstrong was that neither organization’s filings proved a link. There was no definite proof that it was the same money. The IRS forms filed by the groups are pretty scanty—they require organizations to list donations but not the donor—and Armstrong had to work with sources to confirm the connection.

It took a while for Armstrong to establish the link, but he did so in a November 17, 2010, story. Neither group would confirm that it was the same money—the Chamber still won’t—but no one called for a correction.

“Giving money to the Chamber lets you have it both ways,” Armstrong said. “You can sit with the Democrats, lobby for your position, and have your phone calls returned. At the same time, you have someone like the Chamber out there, running ads, doing the public relations campaign.”

After his first story, Armstrong looked into how the Chamber used the money. He found that it set up a sophisticated operation to oppose the law, particularly in swing states. The Chamber paid for ads that ran in twenty-one states beginning in August of 2009. The ads warned that the government-proposed plan would lead to tax increases, swell the deficit, and expand “government control over your health.”

John Sullivan , a former reporter for The New York Times and The Providence Journal, is a freelance journalist. This story is being jointly published with ProPublica.