A hallmark of government by special interest is the revolving door that allows skilled operators to move back and forth between tax-paid jobs in the executive and legislative branches when the Democrats are in power, and private sector organizations devoted to political and ideological agendas when the party is out of power.

David Doniger and Cathy Zoi provide excellent illustrations of how the revolving door works.

Doniger is currently policy director of the Washington climate center of the Natural Resources Defense Council, but his career path during the past two decades has taken him back and forth through the revolving doors.

He first began working at NRDC in 1978 and remained there for the next 14 years, helping to win the 1987 Montreal Protocol and the 1990 Clean Air Act amendments. In 1992, he joined the Clinton administration, where he was counsel to the head of the U.S. Environmental Protection Agency's clean air program and later, the agency's director of climate change policy.

Doniger spent a year at the Council on Environmental Quality, then rejoined NRDC in March 2001 in his present position. As part of his work with NRDC, Doniger heads a legal committee that litigates against rules he helped write while in government.

On the NRDC blog, Doniger notes that "now we're working to pass legislation to cap and cut the pollution that causes global warming, and to reach a new treaty for global emission cuts."

Then there's Zoi, currently President Obama's assistant secretary for energy efficiency and renewable energy in the U.S. Department of Energy. Like Doniger's, Zoi's career path has seen several trips through the revolving doors.

During the early years of the Clinton administration, Zoi was chief of staff in the White House Office on Environmental Policy in 1994 and 1995, then went over to EPA in 1995 where she pioneered the government's Energy Star program.

Zoi spent some years working overseas, serving as assistant director general of the New South Wales EPA in Sydney, Australia, from 1996 to 1999. And she spent some time from 2003 to 2007 as group executive director at the Bayard Group (now Landis+Gyr Holdings), a world leader in energy measurement technologies and systems.

In 2007, Zoi became chief executive officer of former Vice President Gore's Alliance for Climate Protection, remaining there until 2009 when she rejoined the federal government as an Obama appointee.

Going back and forth through the revolving doors is not without risk, though. Zoi's husband, Robin Roy, is vice president of projects and policy for Serious Materials, a company specializing in energy efficient building materials.

The Zois own 120,000 shares in Serious Materials and, as an officer of the company, Roy receives options on an additional 2,500 shares every month and will continue to do so until October 2012.

The Zois own between $250,000 and $500,000 in "founders shares" and another $15,000 to $50,000 in ordinary shares in Landis+Gyr, which makes smart meters, the advanced devices that enable real-time energy usage monitoring for greater efficiency and responsiveness by utilities and other price-setting agencies.

Cathy Zoi has not responded to specific requests asking if she has recused herself from all Energy Department actions that might affect her investments or those of her husband.

Examiner Columnist Ron Arnold is executive vice president of the Center for the Defense of Free Enterprise, and author of Undue Influence and Freezing in the Dark.