But to argue, as Mr Obama does, that he offers something completely new may be to overstate his case a little. Each of his three central messages is as old as the Republic - the promise of bipartisanship ("to put an end to the bickering and the partisan ways of Washington"), an ethical foreign policy ("to restore America's moral place in the world") and delivering change through unity ("to stand up and say we are one nation; we are one people; and our time for change has come")
Each of these themes also share two traits. First they are drawn from the school of "American exceptionalism" - the belief that America offers a uniquely moral beacon to the world. And second, they are virtually impossible to accomplish.
There is nothing inherently accident-prone about American exceptionalism - for every Iraq war there is a Marshall Plan. And there is nothing wrong with promising things you cannot fully deliver. It is better to get some of the way there than never to try at all.
But it may also be necessary to manage expectations a little if your supporters are as fired up as those of Mr Obama. At the moment, Mr Obama is doing the opposite. While often beautifully pitched, his words often veer close to the prophetic. Take Mr Obama's speech last Tuesday night to supporters in Chicago.
"We are the ones we have been waiting for," he said in a paraphrase of Oprah Winfrey's disclosure that Mr Obama was "the one, the one I have been waiting for".
Mr Obama continued: "We know that what began as a whisper has now swelled to a chorus that cannot be ignored, that will not be deterred, that will ring out across this land as a hymn that will heal this nation, repair this world, make this time different than all the rest."

Or take Mr Obama's victory speech after the caucuses in Iowa that kicked off the primary season: "On this January night - at this defining moment in history - you have done what the cynics said we couldn't do. In lines that stretched around schools and churches, in small towns and big cities, you came together to say that we are one nation, we are one people and change is coming to America."

It was a poetic speech that one commentator memorably described as a "goose-bump" moment. But if getting the votes of 95,000 mid-westerners is a defining moment in history, in what terms would Mr Obama describe his nomination?

Should have pursued a career a TV evangelist. With the Obama gift of gab, he could become wealthiest man in the world.