In campaign literature and speeches, each of the three leading presidential candidates has trumpeted the experience that makes him or her best suited for the job.
A biography on Sen. John McCain's campaign Web site proclaims his "remarkable record of leadership and service." Sen. Barack Obama's Web site describes the "rich and varied experiences" of his life. Sen. Hillary Clinton has spoken of her "35 years of change" and told supporters, "We need a president who understands the magnitude and complexity of the challenges we face and has the strength and experience to address them from day one."
But history shows that there is no clear correlation between experience in elected office and presidential success.
"It's not just how much experience they had, but where and how they got that experience," said Stephen Hess, a senior fellow emeritus at the Brookings Institution and an expert in presidential history.
For example, few presidents can boast of a resume as impressive as that of James Buchanan. He spent five terms in the U.S. House of Representatives and a decade in the Senate; he was minister to Great Britain and secretary of state. Yet by all accounts, he was a terrible president, unable to quell divisions between the North and South that led to the Civil War.
In contrast, Abraham Lincoln, a self-taught lawyer whose entire experience in public office consisted of eight years in the Illinois Legislature and one term in the U.S. House, is considered one of the greatest presidents.
"[He] was just really superb at understanding the crisis of the time and understanding how to get along with people," Goucher College history professor Jean Harvey Baker said.
An unlikely candidate, Lincoln was elected only because secession had split the parties and disrupted the political machine, scholars say.
Lincoln was "a towering genius who could have never made it during a normal election," said Brown University historian Ted Widmer, adding that he "came at exactly the moment we needed him."
Although other presidents with thin resumes proved to be capable leaders, Lincoln is an extreme example. As Widmer says: "I don't think it's so realistic to think there are a lot of Abraham Lincolns floating around out there."
The first nation's six presidents were extremely qualified, including in their ranks the commanding general during the American Revolution (George Washington), the primary writer of the Declaration of Independence (Thomas Jefferson) and a principal architect of the Constitution (James Madison).
Although many of these men are considered among the country's greatest leaders, the sixth, John Quincy Adams, was a marginally successful president, despite having distinguished himself in many prestigious posts.
The presidents of the 19th century, with the notable exception of Lincoln, are a largely unremarkable lot. Their backgrounds -- some senators, governors, war heroes and a smattering of vice presidents -- are typical for the nation's leaders.
The first great president of the 20th century, Theodore Roosevelt, has one of the most eclectic resumes. A Harvard graduate, he operated cattle ranches in what was then called the Dakota Territory, led the Rough Riders in the Spanish-American War and served as New York City police commissioner and assistant secretary of the Navy.
He was elected governor of New York in 1898 and, in 1900, vice president. When William McKinley was assassinated six months later, Roosevelt became president.
"This may look like a lack of political experience, but he learned a lot by being on the ground," said Rice University history professor Douglas Brinkley, adding that Roosevelt's time in the West and fighting in the war helped him make wise decisions about land preservation and the military.
In the decades following Roosevelt, presidents with some of the most diverse backgrounds were elected.
Woodrow Wilson, the former head of Princeton University, is the only president to have earned a doctoral degree -- from the Johns Hopkins University. His successor, Warren G. Harding, was a newspaper publisher.
Herbert Hoover, an engineer and businessman who had directed the relief effort in Europe after World War I, led the nation as it plunged into the Great Depression.
"It's kind of the opposite of the Lincoln argument," Widmer said. "An outsider came in and was a very unsuccessful president."
Hoover's successor, Franklin D. Roosevelt, achieved greatness not because of his political experience -- he had been a New York state assemblyman, assistant secretary of the Navy and a one-term governor -- but because of his personal life, especially his crippling bout of polio, historians say.
"As a human being, his struggle against his infirmity is just as important as his experience in politics," Baker said.
Character and charisma also propelled the careers of John F. Kennedy and Ronald Reagan, scholars say.
A president's background -- whether as governor, senator or soldier -- has a marked influence on his leadership style in the Oval Office, historians say.
"Governors are more used to being the executive. Even if they're from a smaller state, they know how to delegate well, hire and fire, stay within budgets," Widmer said. "Senators are more used to working within the system, which can be a good thing."
Former vice presidents come into office with the best understanding of the executive branch but struggle to create their own legacy, Hess said.
Military leaders have the most experience running a large bureaucracy, he said, citing Dwight D. Eisenhower as an example.
Although the three front-runners in this year's election are all senators, it is their life stories, not their political achievements, that make them appealing to voters, scholars say.
"For all three of them, their Senate careers are not what people are looking at," Brinkley said, noting that "workhorse" senators Joseph R. Biden Jr. and Sam Brownback dropped out of the race early.
Each of the candidates is unique in U.S. history -- Clinton because she is a woman, Obama because he is black and McCain because of his experience as a prisoner of war -- and there are no easy predictions about how they will perform in office, Widmer said.
"It's a fascinating, volatile moment and no one knows what's going to happen next," he said. "And that's good for democracy, too."
STRONG RESUME / BAD PRESIDENT
On paper, James Buchanan had strong credentials to be president. A Dickinson College graduate and a lawyer from Lancaster, Pa., Buchanan served in both houses of Congress. He was secretary of state under James K. Polk and minister to Great Britain under Franklin Pierce. In the White House, however, he was dreadful. Buchanan presided over a crippling financial panic, failed to oppose the expansion of slavery and allowed the country to drift toward secession and civil war. Historians rate him among the worst presidents.
THIN RESUME / GREAT PRESIDENT
From a humble background, largely self-taught, "Honest Abe" Lincoln was a village postmaster and storekeeper who became a successful lawyer. An Illinois state legislator and a one-term U.S. representative (who opposed the U.S.-Mexican War), he failed twice to win election to the U.S. Senate. In 1860, with the vote split among four candidates, Lincoln was elected president. With rare vision and courage, Lincoln led the Union through the devastation and heartbreak of the Civil War and laid the foundation for the modern United States. Many consider him the greatest of our presidents.
MIDDLING RESUME / GREAT PRESIDENT
Hyperactive Teddy Roosevelt juggled many interests and enthusiasms on a fitful path to the White House. The son of a rich New York family, Roosevelt was a state legislator, a cattle rancher, a failed candidate for mayor of New York, a civil service commissioner and a reform-minded head of the city's Board of Police Commissioners. He was briefly assistant secretary of the Navy, an officer in the Spanish-American War and governor of New York. He was tapped to be William McKinley's running mate in 1900 largely because New York's Republican bosses wanted to get rid of him -- never dreaming that, within a few months, McKinley would be dead. Roosevelt gloried in the "bully pulpit" of the presidency, and his accomplishments across a broad spectrum -- taking on the "trusts" that controlled large sectors of the U.S. economy, pushing for laws to protect the public health and welfare, creating national parks and negotiating an end to the Russo-Japanese War, to name just a few -- are little short of astonishing.
MIDDLING RESUME / GREAT PRESIDENT
Franklin D. Roosevelt
Franklin Delano Roosevelt, from New York's Hudson River aristocracy, was rich and charming -- and shameless in exploiting his distant kinship with Teddy Roosevelt. Like Cousin Teddy, he was a Harvard man, a state legislator, assistant secretary of the Navy -- and he married Teddy's niece Eleanor. In 1920, largely on the strength of the Roosevelt brand, Franklin was chosen as the running mate of Democratic presidential nominee James M. Cox. Cox lost. Soon after, Roosevelt was stricken with polio. Roosevelt's struggle to regain his strength no doubt gave him useful insights into the challenges ordinary people had to face. In 1928, Roosevelt made a political comeback and was elected governor of New York. Four years later, at the height of the Great Depression, Roosevelt defeated President Herbert C. Hoover to win the first of four races for the White House. Roosevelt led the country out of the Depression through World War II. The longest-serving president, he is usually ranked among the greatest.