What makes a leader?
We examine this year's leading presidential candidates through that prism.
Our leadership categories are adapted from standards developed by Fred Greenstein, a Princeton scholar and author of "The Presidential Difference."
Greenstein says the modern presidency is so powerful, voters should take careful stock of the strengths and weaknesses candidates might bring to the job — from their psychology, emotional maturity and vision to the way they process information, manage and communicate.
Using Greenstein's work as a jumping-off point, we assess candidates in the following areas: political skills, communication skills, policy vision, decision-making style and management skills.
The eight profiled candidates have double-digit support in the latest national USA TODAY/Gallup Poll.
Not every presidential candidate would embrace an unpopular war policy or, in the heat of the Republican primary, team up with one of America's best-known liberal Democrats to propose a pathway to legal status for millions of undocumented immigrants.
Or take positions on campaign finance reform, tax cuts and climate change diametrically opposed to his party's activist base.
Or denounce certain leaders of the Religious Right, a powerful influence on Republican politics, as "agents of intolerance."
Or criticize federal subsidies for ethanol, the corn-based fuel additive that is a sacred cow in Iowa, traditional home of the nation's first caucuses.
But John McCain, a four-term senator from Arizona, has risen to national prominence with a reputation as a politician who does it his own way.
"The word 'maverick' was invented for him," says Larry Sabato, director of the Center for Politics at the University of Virginia.
McCain was widely described as an insurgent Republican when he nearly upset GOP front-runner George W. Bush in 2000. He continues to cultivate his independent image, despite his intimate association with President Bush's current Iraq war strategy.
While never wavering in his call for victory and warnings about the consequences of defeat, McCain points out that he alone among the leading 2008 Republican hopefuls has a record of condemning former Defense Secretary Donald Rumsfeld's "terrible mismanagement" of the conflict.
"I'd rather lose a campaign than lose a war," McCain often says when discussing the effect of his Iraq war support on his White House candidacy.
This is the delicate line McCain must walk as he attempts to retain the moderate and independent voters who backed him in 2000 while trying to also appeal to the conservatives central to the GOP nominating process.
McCain's maverick behavior has consequences. He downplays his past attacks on ethanol by joking that he drinks "a glass of ethanol every morning before breakfast," but he continues to lag in Iowa, a state he skipped in 2000.
His attempts to patch up old feuds with the evangelical Christian community turned off many old admirers. At the same time, many social conservatives continue to distrust him.
McCain tries to convince Republican voters that he has learned a lesson from the outcry over his recent collaboration with Sen. Edward Kennedy, D-Mass., on the immigration bill. McCain now promises he will not pursue a temporary-worker program or other perceived benefits for illegal immigrants until the borders are secured.
"He hasn't changed his core beliefs as to what needs to be done," says Sen. Jon Kyl, R-Ariz., who is active in McCain's presidential campaign. "But he recognizes that until there is better evidence of enforcement, people are not of a mind to look to other solutions."
McCain's political prowess was evident in 1982 when, with few Arizona ties, he won a hotly contested congressional seat. Later, he weathered a political typhoon as a player in the Keating Five scandal and handily won re-election to the Senate. He was able to defeat the better-financed Bush in the 2000 New Hampshire primary by nearly 20 percentage points.
One chief asset is McCain's media savvy. Packing his campaign bus with reporters bolstered his long-shot 2000 campaign and made the Straight Talk Express a modern American political icon. Media allies helped him push his McCain-Feingold campaign-finance reform legislation into law in 2002 over the reservations of Bush and congressional GOP leaders. Frequent appearances on the Sunday public-affairs programs keep McCain in front of TV viewers when tight campaign dollars limit his advertising.
McCain's Straight Talk Express campaign bus has reached out to a new breed of media passenger: the political blogger.
"It's only natural to like a politician who is constantly accessible, who answers all of your questions and who even converses with you not as if you were an enemy or an annoyance but as if you were a guest at his house," wrote conservative Power Line blogger Paul Mirengoff, who recently traveled on McCain's bus in New Hampshire.
Sometimes John McCain delivers what he bills as the unvarnished truth with humor. Other times, he's deadly serious.
At town hall meetings on the campaign trail, McCain is funny, self-deprecating and irreverent. He cheerfully takes on all challengers in the crowd.
Debates have proved a mixed bag for McCain. When he's "on," he's tough to beat. Too often, though, at least in the early debates, McCain came across as stiff and scripted.
Delivering prepared remarks presents other challenges. He is clearly uneasy reading from a teleprompter, and even well-written speeches sometimes are obscured by his dreary delivery.
"I would not let John McCain have one note card up there," says Grant Woods, a former McCain congressional chief of staff who later served two terms as Arizona's attorney general. "Just let him be himself. When he does that, he's just fantastic."
Something else doesn't always survive the translation: McCain's wisecracking sense of humor.
When McCain quipped that a Concord, N.H., high school student was a "little jerk" and was "drafted" for asking him if he worried about contracting Alzheimer's disease, the crowd roared its approval. However, many news outlets reported the remark as if McCain angrily lashed out at the teen.
When McCain jokingly sang "bomb, bomb, bomb, bomb, bomb Iran" to the tune of the Beach Boys' hit "Barbara Ann," peace activists reeled in disbelief.
McCain suggests his critics need to lighten up.
"You can't be a loose cannon, but you've got to have fun," McCain said.
Sometimes McCain's humor hits the bull's-eye. His line about missing the 1969 Woodstock rock festival because he "was tied up at the time" as a prisoner of war in Vietnam brought down the house at the Oct. 21 Republican debate in Orlando
John McCain quite literally is a student of decision-making.
His latest book with co-author Mark Salter is "Hard Call: Great Decisions and the Extraordinary People Who Made Them." McCain and Salter examine the qualities of historic decision-making such as foresight, confidence and humility.
In the book's introduction, McCain gives little insight into his own decision-making process.
"The ways I have arrived at important decisions, both right and wrong ones, have varied over the years," McCain writes. "I hope this has resulted in a progressively better approach. But I have blundered often enough in recent years to foreswear such a boast."
McCain staked out lonely ground on the GOP presidential campaign trail with his early and vocal support of President Bush's surge strategy in Iraq and his push for bipartisan comprehensive immigration reform.
"He looks back and has some confidence that choosing the right path, or following the right policies, will win out even on occasions when at first glance it might look like a loser," says Scott Celley, a McCain Senate spokesman in the late 1980s and early 1990s.
When McCain fails to follow what he believes is right, it usually backfires.
During the 2000 campaign, McCain was asked to comment on the controversy over South Carolina's continued flying of the Confederate flag at its Capitol.
After initially acknowledging that many Americans reject the Confederate flag as an offensive "symbol of racism and slavery," McCain allowed political advisers to talk him into amending his statement to avoid offending the flag's supporters.
That political compromise still gnaws at McCain, who wound up losing to Bush in the South Carolina primary anyway.
"I had been a coward, and I had severed my interests from my country's," McCain wrote in his 2002 memoir, "Worth the Fighting For." "All my heroes, fictional and real, would have been ashamed of me."
McCain regularly taps others for advice in making political decisions.
"I have a wide circle of people that advise me," McCain said in an interview on his "No Surrender" bus tour in September.
Celley said McCain's reliance on "a multidisciplinary collection of aides" dates back years but adds that the most important factor always has been the incredibly well-read McCain himself.
"He sucks up information," Celley says. "You can overload some people on Capitol Hill and elsewhere on facts and details. You can't (overload) John McCain. He can make a decision even as he is getting new information and moving forward on a developing issue."
John McCain often finds himself crosswise with members of his own party and doesn't hesitate to seek bipartisan fixes to problems.
In the early 1990s, chastised by his own embarrassing link to the Keating Five scandal, McCain emerged as a national reformer. He not only took on the big money campaign-finance system but also free-spending congressional appropriators, the tobacco companies and others McCain felt stood in the way of his good-government agenda.
During his 2000 presidential race, McCain ran as a progressive Republican in the style of President Theodore Roosevelt, one of his personal heroes. He stressed patriotism and advocated for a muscular foreign policy.
Between then and now, terrorists crashed hijacked planes into the World Trade Center and the Pentagon. In his 2008 campaign, McCain solemnly calls "the war against Islamic extremism" the overarching challenge of the generation.
From the stump, he lashes out at corrupt members of Congress and lobbyists. In TV ads, he blasts federal pork-barrel spending and government waste. He is the strongest champion on the Republican side for confronting global warming.
Generally speaking, McCain supports limited government and would like to give the states more autonomy.
An example is McCain's position on same-sex marriage. He believes it's a state matter and would back a federal constitutional amendment banning same-sex marriage only if the courts intervene at the state level.
McCain is in his fourth term in the Senate. Before that, he served two terms as an Arizona member of Congress. That followed a Navy career that included more than five years as a prisoner of war during Vietnam.
But one glaring hole in his resume is a lack of the sort of executive management experience one would get as a governor, a big city mayor or even the chief executive of a corporation.
McCain points out he does have some relevant experience beyond managing his Senate office and the Senate commerce and Indian Affairs committees that he has chaired. His Navy years included a stint as commanding officer of a squadron.
"I didn't manage it — I led it," McCain said at a Sept. 5 debate in Durham, N.H.
But critics look to McCain's presidential campaign, which underperformed, overspent and nearly went bankrupt this summer. An internal shake-up led to the resignations of Terry Nelson, his campaign manager; John Weaver, his longtime political strategist; and a massive staff downsizing.
"It's perfectly reasonable to judge a presidential candidate's management skills by how he or she runs the campaign," political scientist Larry Sabato says. "Obviously, McCain didn't do so well."
Others say McCain's long history on Capitol Hill should convince voters that he knows what he's doing.
Former spokesman Scott Celley compared McCain with President Eisenhower, who also entered politics from the military, albeit with higher rank and responsibility. Eisenhower was an Army general, McCain a Navy captain.
Anybody who rises through the military chain must display "some degree of management and organizational acumen," Celley says.