Sen. John McCain presented a memento to fellow Republican Sen. Ted Stevens when they met in the Senate earlier this year: a key chain with a small battery-operated pig's head.

"You're still an oinker," the presidential candidate told Stevens, the Alaskan renowned for legislative pork that benefits his state.

A Stevens spokesman said the gesture was taken in good humor, though McCain's crusades against federal waste have pricked Stevens before.

That is perhaps as nicely as McCain plays. The key chain incident reflects two defining characteristics of his time in Congress that some say help explain his poor showing early in the 2008 race for the White House.

FOR THE RECORD: An article published April 26, 2007, about what Sen. John McCain's reputation as a political maverick might mean for his chances in the 2008 presidential race said that President Theodore Roosevelt lost his party's nomination in the election following his second term. Roosevelt lost the nomination three years after his second term had ended.

McCain, who formally announced his candidacy Wednesday, has staked out a career in oversight, investigation, reform and old-fashioned muckraking. He has done it aggressively, sometimes with personal attacks. Careers have been destroyed in the process.

And he has often damaged the fortunes of the Republican Party. His investigation into the recent lobbying scandal helped label the Republicans as the "party of corruption" heading into the 2006 elections, in which the GOP lost control of Congress.

Though McCain's investigations have uncovered plenty of government sleaze and made him a hero to many independent-minded Americans, political historians say this barely registers on election day. Reformers have rarely ascended to the White House, analysts say, because their passions are often too narrow to galvanize voters.

Meanwhile, the pain McCain has caused fellow Republicans has cost him a reservoir of support against political headwinds -- as now, when he doggedly backs the Bush administration's policy on Iraq in the face of overwhelming voter opposition.

"You don't win a lot of votes from Republicans by investigating Republicans," observed George C. Edwards III, a political scientist at Texas A&M University. "He can't go to Republicans and say, 'There is a lot of corruption in Washington and I have been cleaning it up,' when the Republicans have been running it. That's not an applause line."

A former Navy pilot and war prisoner in North Vietnam for six years, the son and grandson of admirals, he was first elected to the House in 1982 and the Senate in 1986 in Arizona. He built a reputation as a straight shooter and staunch conservative, but one who was fiercely independent of party lines.

Early in his Senate career, McCain was one of the "Keating Five," a group of senators who were disciplined for improperly trying to influence federal regulators in the savings and loan scandal of the late 1980s. Some say this triggered his crusade against government corruption. The incident was "one of the worst experiences of my life," McCain later wrote.

Through his positions on three Senate committees, McCain has gone after a wide range of targets: the Air Force, a powerful Republican lobbyist, members of Congress, NASA officials, Firestone tires, Boeing aircraft, campaign fundraising and much more.

In the process, he has helped topple Cabinet secretaries, top military officers, a once-influential Christian conservative, Republican leaders in Congress, defense industry executives, congressional staffers and others.

"Just his name is enough to make people stand up and take notice," said Alan Ladwig, a former associate administrator of NASA. "He could make your life miserable."

Others are more severe, accusing McCain of being vindictive and manipulative in his investigations.

On the other hand, many government watchdog groups credit McCain with saving taxpayers billions of dollars, improving public safety, stopping illegal influence-peddling and protecting Indian tribes.

"He is fantastic," said Danielle Brian, executive director of the Project on Government Oversight. "It takes a special level of courage to do oversight. But it does make enemies."

Indeed, McCain the candidate doesn't tout his reform efforts, even though they are the hallmark of his political career. Reform is complicated, obscure and transitory.