No one would accuse Carl Levin of looking like Hollywood's version of a U.S. Senator. He's pudgy, balding and occasionally rumpled, and he constantly wears his glasses at the very tip of his nose. Still, the Michigan Democrat has gained respect from both parties for his attention to detail and deep knowledge of policy, especially in his role as a vigilant monitor of businesses and federal agencies. In 2002, a subcommittee he led hauled in Enron's board of directors to question them about the company's shady accounting practices; in hearings a year later, he was one of the chief challengers of large accounting firms that had created illegal tax shelters. Congress passed laws in the wake of both scandals in an effort to prevent the abuses from happening again.

America's Best Senators Those who do, and don't, make a difference in the U.S. Senate The Best Senators Thad Cochran Kent Conrad Dick Durbin Ted Kennedy Jon Kyl Carl Levin Richard Lugar John McCain Olympia J. Snowe Arlen Specter The Worst Senators Daniel Akaka Wayne Allard Jim Bunning Conrad Burns Mark Dayton From the TIME Archive Nov. 5, 1979 The Kennedy Challenge More than a quarter century ago, TIME covered the presidential campaign of Senator Ted Kennedy, "the last of the Kennedy brothers, the youngest, the most vulnerable, the most thoroughly political"

Levin, 71 and first elected in 1978, says he considers congressional hearings a critical part of his job, spending as much as 20 hours prepping for each one so an evasive witness won't outwit him. The former civil-rights lawyer is known for forcing embarrassing admissions from Homeland Security Secretary Michael Chertoff and other Bush Administration officials through his precise questioning. "You've got to be very blunt and truly listen so you know when the b.s. is flying," Levin says.

Although admired by many Republicans for his diligence, Levin rarely sides with them. He opposed the Iraq war, and as the top Democrat on the Senate Armed Services Committee, he has become one of his party's leading voices in criticizing President Bush's conduct of the invasion, arguing that the Administration didn't have enough troops in the early stages and, more recently, hasn't focused enough on training Iraqi troops. But his carefully researched, thoughtful remarks carry great weight with his colleagues. "Nobody in the Democratic Caucus says anything on national-security issues without talking to Carl Levin," says a top Democratic Senate staff member.