Sometimes the power of a law depends on the lawmaker. Last May the Senate unanimously passed a Democratic amendment banning the torture of prisoners in U.S. custody. No one paid any attention. Then in October John McCain introduced his antitorture amendment, using identical language, and the issue landed on the front pages of newspapers across the country. The White House jumped to attention, dispatching Vice President Dick Cheney and National Security Adviser Stephen Hadley to try to talk McCain down. He stood firm, and the bill passed unanimously in December.

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"

It wasn't just that McCain, 69, had been tortured as a prisoner of war in Vietnam. McCain has that rare ability to put an issue on the U.S. agenda that wouldn't naturally be there. "It's a question of moral authority," says former New Hampshire Senator Warren Rudman of his former colleague. McCain has earned that moral authority over the years by being patient and making the big play. Many of the problems McCain tackles are entrenched and unexciting: they challenge the rules in Washington and the cynicism of voters at home. Over the past decade, McCain forced through a reform that made the money coming in from rich interest groups and directed at political advertisements more transparent. He has spent his entire Senate career exposing wasteful pork-barrel projects. And in the past year, he took his backwater committee, Indian affairs, and used it to launch an investigation of lobbyist Jack Abramoff, whose admission in federal court that he conspired to bribe public officials produced a series of efforts to ban certain kinds of influence peddling.

The skills that allow McCain to put unorthodox issues at center stage—independence, single-mindedness—don't always translate well to other pursuits. They helped McCain lose the 2000 G.O.P. presidential primary by scaring the party establishment and its base. So as the front runner in the 2008 campaign, McCain is taking the opposite tack, endorsing Bush tax cuts that he once opposed as fiscally unsound; embracing religious conservatives like Jerry Falwell, whom he once denounced; and endorsing the teaching of intelligent design as an alternative to evolution. Opinion writers have been perplexed at the preprimary turnaround, but the two-year walk-up to 2008 won't just consist of courting the party's die-hards. McCain is scheduled to assume the chairmanship of the powerful Senate Armed Services Committee next January, a target-rich environment for a waste and fraud hunter. He is already stumping against gerrymandering, which he says is undemocratic. "It's harder to keep your job in the politburo in Havana than in the House of Representatives," McCain says.

And if he wins in 2008? Among the first items on his agenda in 2009, McCain says, is winning the battle that George W. Bush just lost—fixing Social Security and other underfunded entitlements. Crucial to that effort, he says, is getting Congress to clean house. "If you've got $47 billion in earmarks and 6,140 pork-barrel projects on the highway bill, how can you expect the American people to make tough decisions about entitlement programs?" he asks. No matter what happens in '08, says scholar Norman Ornstein, McCain will be remembered as "one of the few people who can have great impact in the Senate."