In 2009, Congress set out to require that investment partnerships like hedge funds register with the Securities and Exchange Commission, partly so that regulators would have a better grasp on the risks they posed to the financial system. The early legislative language would have required single-family offices to register as well, exposing the highly secretive institutions to scrutiny that their clients were eager to avoid. Some of the I.R.S.’s cases against the wealthy originate with tips from the S.E.C., which is often better positioned to spot tax evasion. By the summer of 2009, several family office executives had formed a lobbying group called the Private Investor Coalition to push back against the proposal. The coalition won an exemption in the 2010 Dodd-Frank financial reform bill, then spent much of the next year persuading the S.E.C. to largely adopt its preferred definition of “family office.” So expansive was the resulting loophole that Mr. Soros’s $24.5 billion hedge fund took advantage of it, converting to a family office after returning capital to its remaining outside investors. The hedge fund manager Stanley Druckenmiller, a former business partner of Mr. Soros, took the same step. The Soros family, which generally supports Democrats, has committed at least $1 million to the 2016 presidential campaign; Mr. Druckenmiller, who favors Republicans, has put slightly more than $300,000 behind three different G.O.P. presidential candidates. A slide presentation from the Private Investor Coalition’s 2013 annual meeting credited the success to multiple meetings with members of the Senate Banking Committee, the House Financial Services Committee, congressional staff and S.E.C. staff. “All with a low profile,” the document noted. “We got most of what we wanted AND a few extras we didn’t request.”