Raised on a Montana ranch, Sen. Max Baucus now wrangles tax policy as head of the powerful Finance Committee. The Big Sky State Democrat, 69, was elected to the U.S. House in 1974, and made the jump to senator four years later. He is currently the fifth-longest-tenured senator and the third among Democrats.

As the wars in Afghanistan and Iraq march toward a second decade, Democrat Carl Levin chairs the Senate committee overseeing the Defense Department. Levin, now 76, is in his sixth term and has represented Michigan in the Senate since 1979 — the longest tenure of any Michigan senator in history.

As Washington struggles to cope with unprecedented deficits and an influx of Tea Party conservatives, perhaps no one will be under the microscope more than Senate Budget Committee chairman Kent Conrad, a North Dakota Democrat. Referred to by The Bismarck Tribune as “the most influential senator North Dakota has ever produced,” Conrad helped write the 2002 and 2008 farm bills, played an active role in comprehensive energy legislation, and helped craft the 2008 financial bailout package. But those accomplishments may pale in comparison to the challenges ahead.

Debbie Stabenow accepts the gavel for the Committee on Agriculture, Nutrition, and Forestry just as preparations begin for what is sure to be a controversial new farm bill in 2012. Stabenow, the junior senator from Michigan, is currently in her tenth year in the Senate, following a four-year stint in the U.S. House and 16 years as a state legislator. A former social worker and part-time folk singer, Stabenow, now 60, was first elected to public office at age 24.

Daniel Inouye, the 86-year-old Senate Appropriations Chairman, doesn’t shy away from his big-spending ways — he brags about it. “It may please you, or it may not please you,” he told business leaders in his home state of Hawaii in 2009, “I’m the number one earmarks guy in the U.S. Congress.”

As federal regulators begin to implement financial regulatory reform, Tim Johnson of South Dakota replaces retiring Sen. Chris Dodd in the high-profile chairmanship of the Senate Banking, Housing, and Urban Affairs Committee.

Since becoming the first female chair of the Senate Environment and Public Works Committee in 2007, California Democrat Barbara Boxer has focused on combating climate change — calling on former Vice President Al Gore to testify, for instance, and advancing a cap-and-trade bill on carbon emissions. In November 2009, Boxer’s committee approved an energy and climate change bill despite a Republican-led boycott. Ultimately, the comprehensive legislation never made it to the Senate floor for a vote. Even Boxer concedes that Republican gains this past November will make it virtually impossible to pass climate legislation in the upcoming congressional session. But Boxer has made clear she’s in the fight for the long haul.

As chair of the Energy and Natural Resources Committee, New Mexico Democrat Jeff Bingaman has been in the middle of the contentious debate over climate regulation and legislation. Bingaman has long been the Democrats’ leading voice on issues concerning energy production and consumption. The 67-year-old has been the top Democrat on the committee since 1999, serving as chairman from 2001-2003 and again since 2007.

If the results of the closely contested 2000 election had gone slightly differently, Joseph I. Lieberman might have spent at least four years helping to run the executive branch of government. But, instead of becoming the 46th Vice President of the United States, the junior senator from Connecticut has been overseeing the operations of the executive branch as chairman of the Senate Homeland Security and Government Affairs Committee.