For all his experience, McCain has acknowledged that he doesn't know much about the economy, which is the most important issue worrying Americans, according to a USA TODAY/Gallup Poll taken this month.
"The issue of economics is not something I've understood as well as I should," he told reporters in December while campaigning in New Hampshire. He joked, "I've got (former Federal Reserve chairman Alan) Greenspan's book."
Although McCain's campaign has done well lately, it had to recover from an implosion last summer when his top aides left, his poll standing slumped and his campaign bank accounts were mostly exhausted.
•Clinton, 60, has displayed her mastery of the details of domestic and foreign policy in a string of campaign debates. During eight years as first lady, she represented the United States in visits to 80 countries. In seven years as a senator from New York, she's worked on issues from veterans benefits to farm aid, sometimes in alliances with Republicans, and served on the Armed Services Committee.
She describes herself as a strong manager who could ride herd on the sprawling federal bureaucracy — in contrast, she says, to Obama.
"I do think that being president is the chief executive officer," she said at a debate in Las Vegas last month. "I respect what Barack said about setting the vision, setting the tone, bringing people together. But I think you have to be able to manage and run the bureaucracy. You've got to pick good people, certainly, but you have to hold them accountable every single day."
Obama and others say she failed in her chief executive initiative as first lady. Her management of a health care task force early in her husband's presidency produced a controversial overhaul plan that went nowhere.
•Obama says he's proven his good judgment by opposing the Iraq invasion from the start, in contrast to Clinton and McCain. He describes himself as an inspirational leader who can bring opposing forces together to get things done better than "this same old cast of characters" in Washington. He doesn't see the president as being "an operating officer," he says, and would rely on strong advisers to manage the details.
"Now, being president is not making sure that schedules are being run properly or the paperwork is being shuffled effectively," he said at the Las Vegas debate. "It involves having a vision for where the country needs to go."
Even so, Clinton and McCain say Obama offers more soaring rhetoric than solid results and question whether he can claim significant legislative accomplishments or adequate experience.
He served eight years in the Illinois Legislature and has been in the U.S. Senate for three. That's less high-level government experience than any president since Dwight Eisenhower, whose background was in the military.
The five-star general was supreme commander of allied forces in Europe during World War II.
Lincoln or Hoover?
"Maybe (Obama) is Lincoln; maybe he's (the beleaguered Herbert) Hoover. There's no way to tell in advance," says David Frum, a White House speechwriter at the beginning of Bush's tenure who wrote an account of his early presidency, The Right Man. However, that's probably not the decisive question, Frum says.