Because finding ways for wealthy people to give money to politicians is “how this business works.”

Most donors, including Dr. Mohlenbrock and Mr. Kiani, declined to talk about their motivations for giving. But Patrick J. Kennedy, the former representative from Rhode Island, who donated $35,800 to an Obama re-election fund last fall while seeking administration support for a nonprofit venture, said contributions were simply a part of “how this business works.”

“If you want to call it ‘quid pro quo,’ fine,” he said. “At the end of the day, I want to make sure I do my part.”

Mr. Kennedy visited the White House several times to win support for One Mind for Research, his initiative to help develop new treatments for brain disorders. While his family name and connections are clearly influential, he said, he knows White House officials are busy. And as a former chairman of the Democratic Congressional Campaign Committee, he said he was keenly aware of the political realities they face.

“I know that they look at the reports,” he said, referring to records of campaign donations. “They’re my friends anyway, but it won’t hurt when I ask them for a favor if they don’t see me as a slouch.”

So long as government has the power to provide rents for specific interests, interests will seek those rents, campaign finance laws be damned.