AP Photo

With two months to go before the presidential election, the United States is in a seriously bad way. A nation whose hallmark has been a sense of irrepressible optimism and purpose is bitterly divided and uncertain.

According to a Gallup survey, 81 per cent of the American people are dissatisfied with the nation as it is governed and only 24 per cent feel the US is on the right track. That is a historic low.

This widespread despair goes beyond Barack Obama, Mitt Romney, liberal Democrats and Tea Party Republicans. It stems from expectations about America's right to economic prosperity and strategic pre-eminence that no president may be able to meet - expectations that have deep roots in America's past.

The American understanding of their history has been that since...