After four years of incessant gloom, a burst of optimism is seizing America. Or at least pockets of it. The Dow Jones index has been dancing at around 13,000, a number last seen in the spring of 2008 when Lehman Brothers was still just about a going concern. Apple has added $100 billion to its value in just the past eight weeks. Unemployment is finally tilting downwards. In Washington, both President Obama and the Republican candidates have been drooling over the same magazine article, published last month in The New Republic, titled Not Fade Away: The Myth of American Decline, which argues that those Americans who doubt their country’s continued success are committing “pre-emptive suicide”.