"Americans don't vote for the guy with the most experience. If that was true, (Richard) Nixon would have defeated (John) Kennedy in 1960," Frum says. Instead, voters want candidates to meet a threshold of readiness that makes them an acceptable risk to elect as president. "What they seem to do is decide, 'Do you have enough?' "
Little time to learn the ropes
The question of readiness matters because presidents often face unexpected challenges in their first weeks and months in office, before there's been much time to install a staff or learn the ropes.
Less than three months after taking office in 1961, Kennedy approved an invasion of Cuba by anti-Castro forces that had been planned during the Eisenhower administration. The Bay of Pigs venture failed disastrously and raised doubts among world leaders about the young American president.
Less than four months after taking office, Harry Truman approved dropping atomic bombs on two Japanese cities — the culmination of a nuclear weapons program he hadn't even been told about as vice president. Six days later, after an immediate death toll estimated at more than 100,000, Japan surrendered. World War II was over.
It's possible no one can be fully prepared for the velocity of the presidency, a point some presidents and their closest advisers acknowledge after they've made it there.
Bill Clinton had been Arkansas governor for 12 years and had been a leading figure in national debates over domestic policy issues. Even so, after he became president in 1993 he quickly became enmeshed in controversies over gays in the military and the White House travel office, among other things. Only after stunning setbacks in the 1994 congressional elections — Democrats lost control of the House and Senate — did he seem to find his footing as president.
George W. Bush had been Texas governor for six years, CEO of oil industry ventures and managing partner of baseball's Texas Rangers before moving into the Oval Office in 2001 — an "MBA president" who would bring corporate decision-making to the job. Less than eight months later, he had to deal with the Sept. 11 attacks.
His job approval rating hit a historic high of 90% in the aftermath, but Bush has seen Americans' assessment of his presidency sour amid questions over whether the war in Iraq was necessary. His job approval rating was 33% in the latest USA TODAY poll.
"The difference between being president and virtually any other job — running a company or being in the Congress or in the Senate or even being a governor — is the breadth and rapidity of decisions that come at you," says John Podesta, who was Bill Clinton's chief of staff. Podesta heads a think tank, the Center for American Progress.
"You need to both be able to chart a course that emphasizes your priorities but (also) be able to handle and manage things that you never even thought of that are coming at you from left field," Podesta says.
"Stuff just happens."
Confronted by crisis
Presidents have faced defining decisions, some unexpected, soon after taking office. Some examples: