It's the most exciting US election campaign for decades but, as a historian, I'm also struck by deeper currents under the surface of events.
Professor David Reynolds
Presenter of America, Empire of Liberty
John McCain: Ardent patriot
My new series for BBC Radio 4 America, Empire of Liberty takes as its title Thomas Jefferson's prediction in the 1800s that the United States would be a great "empire of liberty".
Empire and liberty have been recurrent and often conflicting themes in America's development and I think they're also reflected in this year's rival presidential candidates.
John McCain embodies the martial, imperial America.
The son and grandson of admirals, he was a career navy pilot who nearly lost his life in Vietnam and spent more than five years there as a prisoner of war, enduring brutal torture.
Mr McCain is an ardent patriot, convinced of America's mission in the world and a strenuous supporter of the war in Iraq.
His story reminds us that the United States is a country made by war.
In the 19th Century, the struggle with Mexico in 1846-1848 won the West, and 620,000 Americans died in the appalling Civil War of 1861-1865.
And a succession of 20th-Century wars made and sustained the US as a global superpower, from Pearl Harbor in 1941 to Kuwait half a century later.
Given the number of Americans who have served in these conflicts, it is not surprising that veterans have become one of the most influential lobby groups in American politics.
Barack Obama couldn't be more different from Mr McCain.
His election to the US Senate in 2004 made him only the fifth African-American Senator in history.
Barack Obama does not come out of the southern civil rights movement
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In 2008 he became the first African American to be nominated as a major party's candidate for the presidency.
These statistics remind us that the United States is still striving to make good its resonant promises about being the land of liberty.
The country is still scarred by the legacies of slavery, on which the prosperity of the South rested until the Civil War.
Even after 1865, black Americans, in North as well as South, languished as second-class citizens, victims of discrimination and segregation.
Not until the 1960s were symbols like separate black and white toilets or drinking fountains eliminated across the South.
The historical significance of Mr Obama's campaign is therefore immense.
President Thomas Jefferson envisaged America as an "empire of liberty"
A victory for him on 4 November would help expunge the original sin of slavery from Jefferson's empire of liberty.
Yet one shouldn't push the empire versus liberty framework too far. Because what makes Mr McCain and Mr Obama fascinating is that each is very much his own man, refusing to be type-cast.
As a senator, Mr McCain has adopted positions at odds with the soldier of empire stereotype, for instance on climate change or the treatment of prisoners at Guantanamo Bay detention camp.
Both of these policies have set him against the Bush administration.
Mr McCain's whole campaign in 2008 is predicated on being a maverick man of principle rather than a doctrinaire party loyalist.
And Mr Obama, though African-American, does not come out of the southern civil-rights movement, led by men who were often the descendants of slaves.
He had a white mother and a Kenyan father; he grew up in Hawaii and Indonesia and eventually settled in Chicago.
His commitment to civil rights is clear, yet this is a very different background and orientation from that of, say, the Rev Jesse Jackson - an aspirant for the Democratic nomination in the 1980s - who grew up in South Carolina and became one of Martin Luther King Jr's lieutenants.
Playing to strengths
Mr Obama's unusual CV helps him reach out to whites as a sort of post-racial candidate.
Mr McCain can outscore Mr Obama on "experience" - with 21 years in the Senate against less than four.
Yet neither has any experience of managing a large organisation - as CEO of a business corporation or as governor of a state (the route to the White House for Carter, Reagan, Clinton and George W Bush).
It's an open question how either would cope with running one of the world's largest, most complex and most unmanageable organisations.
But there is one certain rule of US politics - no-one can predict how a candidate will perform once he gets into the Oval Office.
Consider this damning comment by pundit Walter Lippmann about one of those running for the White House back in 1932:
"He is a pleasant man who, without any important qualifications for the office, would very much like to be president."
Lippmann was renowned as one of the shrewdest observers of US politics. And the "pleasant" man?
He was an upper-class paraplegic from New York by the name of Franklin Roosevelt.
Professor David Reynolds teaches 20th Century history at the University of Cambridge.
He presents America, Empire of Liberty on BBC Radio 4. The first series begins on 15 September and will be broadcast from Monday to Friday at 1545BST and in an Omnibus edition on Fridays at 2100BST.
Listen again on the BBC i-Playeror visit the Radio 4 website