This week, House Democrats will decide which of two senior members will chair a key congressional committee during one of those rare periods when genuinely nation-changing legislation may be passed. John Dingell, who has represented metropolitan Detroit since 1955, is the longtime chairman of the Energy and Commerce Committee.

He has been challenged by the panel's second-ranking member, Henry Waxman, who is best known for exposing countless Bush administration misdeeds as chairman of the Oversight and Government Reform Committee. It was Waxman who uncovered much of the administration's suppression and distortion of scientific findings and of prewar intelligence on Iraq.

Why not just leave things as they are? Fundamentally, there are two reasons Waxman would be the better chairman of Energy and Commerce.

First, he is probably the House's most accomplished legislator in three issue areas that are high on the agendas of the nation and President-elect Barack Obama: universal health care, global warming and enhanced consumer protections (no small matter with a steadily rising percentage of our food and medication ingredients coming from China). On environmental questions, Waxman offers a sharp contrast to Dingell, who has long been the primary opponent of stricter standards for auto emissions and fuel efficiency.

Second, Waxman is a legislative genius. Most of his legislative accomplishments came before the 1994 Republican takeover of Congress, when he chaired the health and environment subcommittee of Energy and Commerce. Progressive legislating has been pretty much off the table since then, which is why he shifted focus to Congress' chief investigative committee. Those who have served in Congress for fewer than 14 years weren't around when Waxman greatly strengthened the Clean Air Act and authored the legislation that expanded Medicaid coverage to the poorest children (enlisting Republican abortion-foe Henry Hyde as his partner in the effort). They didn't see Waxman steer to passage the bills that gave rise to the generic drug industry, required uniform nutrition labels on food, heightened standards of care at nursing homes, created screening programs for breast and cervical cancer, provided health care for people with HIV/AIDS, or expanded Medicaid coverage to the working poor.

In the midst of the Reagan era's cutbacks, Waxman expanded the number of working poor eligible for Medicaid a stunning 24 times. He consistently won key Republican backing for these regulatory and programmatic expansions. In fact, The Wall Street Journal's editorial page ran a series of articles complaining of "the Waxman state," in which, horror of horrors, businesses were compelled to meet environmental and consumer protection standards.

Wyoming Republican Sen. Alan Simpson once emerged from a marathon conference committee meeting and noted, "Henry Waxman is tougher than a boiled owl."

Some of Waxman's achievements were to keep bad things from happening. For virtually the entire 1980s, Waxman blocked Dingell and the Reagan administration from weakening auto emission standards. At one point, he blocked a key vote on a bill to debilitate the Clean Air Act by introducing 600 amendments, which he had wheeled into the room in shopping carts. Waxman also led the war on secondhand cigarette smoke. He publicized an obscure EPA report that established secondhand smoke as a carcinogen, uncovered the onetime Philip Morris lab director who had determined that nicotine was addictive, and publicly grilled tobacco company CEOs about their failure to share that fact with the public.

By 1994, Robert Greenstein, then, as now, director of the Center on Budget and Policy Priorities, noted: "Waxman elevates to high art the blend of substantive policy knowledge, advocacy of policy improvements and excellence in strategic execution." Then came Newt Gingrich. The kind of progressive legislating at which Waxman excelled was no longer possible. In time, he remade himself as Capitol Hill's top cop.

Now, after a 14-year winter, it's legislating season again.

Greenhouse gases are rising, the farms and factories producing the things we ingest have been spread across the globe, the number of uninsured has risen. Obama needs an ally on the Hill who can craft bills and obtain votes for the change he's pledged to deliver. He needs a master legislator. He needs Henry Waxman.

Harold Meyerson is editor-at-large of American Prospect and the L.A. Weekly.