THERE'S one more thing I want to say about the "you didn't build that" shingading, and I think a good way to illustrate it is by comparing the fortunes of Mitt Romney and those of his father, George. In many ways, they're a lot alike. George Romney was a smart, industrious man who worked his way up to CEO of a highly profitable and successful company, making him extremely wealthy and giving him the wherewithal to send his son to fancy schools. His son Mitt is also smart and hard-working, had the energy and discipline to capitalise on the advantages life gave him, and became the CEO of a highly profitable and successful company, making him extremely wealthy and giving him the wherewithal to send his own sons to fancy schools.

But while George Romney was a very well-off guy, his son Mitt has ended up vastly richer. Why is that? A lot of reasons, obviously: the different natures of the two companies, the fact that Mitt both owned and ran Bain Capital while George merely ran American Motors, the vagaries of fate. But one of the biggest reasons why Mitt Romney is so much richer than his father is because the incomes of everyone in America's managerial class are vastly higher in 2012, as a proportion of the economy, than they were in the late 1960s. The share of the national income that went to the top 0.01% of earners nearly tripled between 1968 and 2010, from 1.7% to 4.7%. When you look at people who mainly earned their money from salary rather than investments, such as the elder Mr Romney, the increase was even steeper.

What caused this tremendous increase in the share of wealth going to the top 0.01% of earners? To some extent, it was due to implacable changes in the nature of the global economy: the shift of manufacturing jobs to emerging markets holding wages down, increasing returns to education and information technology, financialisation, the superstar economy. To some extent, it was due to political changes: the collapse of labour unions, drastic cuts in top marginal income-tax rates, and so on.

One thing you can't reasonably say, though, is that it's because top managers in Mitt Romney's era are smarter or harder-working than those in his father George's were. Nor can you say that managers these days are generating more growth or jobs for the rest of us; they're generating less. For the most part, America's richest executives today are vastly richer than America's richest executives in 1968 for reasons that have nothing to do with their own merits or sins, or with their contributions to society. Mitt Romney may have built Bain Capital, but he didn't build the income distribution pattern of the US economy.

Or maybe he did, in part. There is an argument to be made that companies like Bain Capital did, in fact, contribute to the widening of income disparities, by extracting more and more of firms' value for private equity and other investors and for top management, and leaving less and less of it available for workers. But I don't think that's an argument you'll hear Mr Romney making.

Anyway, if America's richest are wondering why a majority of Americans favour taxing them more heavily, they may want to look at the above graph for an explanation. Americans see an elite class that seems to be reaping an ever-growing windfall from globalisation, while average workers are being squeezed ever tighter by unemployment and stagnant or falling wages. The income elite don't appear to have done anything to justify their ever-enlarging share of the pie. They seem to have lucked into it. Or rather, there are two theories. The first theory is that America's financial elites are in no way responsible for the forces that are awarding all the gains from economic growth to them, while tossing only occasional scraps to average workers. The second possibility is that America's financial elites are responsible for those forces. Neither of those theories is very politically helpful to Mitt Romney.