SIMON SCHAMA is a restless optimist of our dissatisfied times. Viewers of his TV histories know that his body never stays still if movement is a possibility. On a literary festival stage his elbows put every water glass in peril. His mental leaps - across centuries and continents and art forms - are the mercurial essence of his books on Dutch art, French politics and cultural gardening. A “History” of “The American Future” is just one more hurdle for him, a history of what has not yet happened, a new taunt to critics who, while admiring him for much, hope that one day, surely, he must fall over.

Barack Obama is the man whom Schama hopes will change the future of his American history. Schama is already putting the Obama story into the pattern of the past. Most pages of The American Future are about the people whom historians are supposed to write about, the ones who are dead, men of the War for Independence and the Civil War. But Schama has followed Obama closely around America this year. Scenes from TV studios and town halls set the openings for the bigger pictures.

The first lines of the book make just the sort of statement that historians are not supposed to make - or not at least at work: “I can tell you exactly, give or take a minute or two, when American democracy came back from the dead because I was there: 7.15pm. Central Time. 3 January 2008. Precinct 53. Theodore Roosevelt High.” Mere journalists may think an event to be historic just because they themselves were at it; historians normally look down on us for doing so. Not this time.

The moment Schama has chosen is the tally of the Iowa Caucus in which Barack Obama proved his potential and Hillary Clinton her frailty. If the successful Democrat loses the race for the White House next month, Schama will look reckless. If Obama wins, the historian will still look reckless to some. That is how he likes it. To quote a central character in American historical fiction - he does not “give a damn”.

Schama is scrupulous in matters of fact. But, like all the best historians, he does not expect plaudits merely for accurate application of knowledge. When two facts are put together, as the saying goes, everything is fiction. Schama is a genius of storytelling, a master of the one profession that is allowed to know what happens after the last page is turned. If others deny that such a vision can exist in a history book that is their problem not his.

After the 2008 Iowa Caucus the reader is taken back just a year to Arlington Cemetery where Vice-President Dick Cheney is delivering homilies for America's war dead “like a tank rolling over a cat”. Schama deftly explains the tradition by which American families are buried together with their soldier sons and husbands in Arlington. He is quickly back with the man who inaugurated that act of comfort, Montgomery C. Meigs, the engineer, architect and quartermaster who won the Civil War by ensuring that Lincoln's men had guns, shoes and pants while Rhett Butler's were gone with the wind.

The Meigs dynasty began in America in 1636 - and is still active now: in NBC studios Schama meets General Meigs, a veteran of Bosnia and teacher of a course called “Why Presidents go to war when they don't have to”. One early Meigs with a Cherokee mistress is followed by another who fought for black slavery. The quartermaster himself gets the most attention - while all the time Schama shows the battles between America's simultaneous and conflicting ideals: liberty and oppression, isolation and empire, the simple state without a standing army and the complex state of the military-industrialists.

Obama is brought back to open the chapters on “American Fervour”. When Schama listens to him invoking the American future the historian inevitably hears the American past: but this past “is not a drag-weight on ‘change', just the solid ground beneath the high-sailing rhetoric”. Obama, like Schama, is an intellectual filled with knowledge, pride and optimism: his “attachment to the past is not just cultural exhibitionism, a guaranteed vote-loser in America; rather it's the grace note in Lincoln's ‘mystic chord of memory', the sonority without which appeals to the American spirit in tough times are just so many sound bites”.

Obama's example takes Schama back to his own memories of the 1964 Democratic Convention. His chapter on What is an American? begins with Gordon Brown's implausible invitation to historians to join him at dinner with George W. Bush in Downing Street: “We who had communed in our pages with Churchill and de Gaulle would now sprinkle a little Significance around like air-freshener in the parlour of exhausted power.” Nicely said. When Schama and the president get to agree on a liberal immigration policy for Mexicans - in the best tradition of American history - the evening is almost a success, the account of it leading to a bravado disquisition on the “melting pot” then and now.

The book ends in a meeting with a fellow optimist, an Islamic American called Chuck, an “American who happens to have some Lebanese blood and who is a Muslim”. The mere fact of the Obama candidacy, “with roots in Muslim Kenya and Christian Kansas is a source of happy marvel to him: a vindication of America whatever the outcome of the presidential election”.

Schama himself will feel properly vindicated only if Obama wins. A historian who radiates such anticipated pleasure is a rare thing. We are lucky to have him.

The American History: A Future by Simon Schama
Bodley Head, £20; 400pp Buy the book

The Times Cheltenham Literature Festival: Simon Schama examines America's future: October 10, 6.30pm
cheltenhamfestivals.com

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