When a group of millionaires appear onstage with a Democratic President to call for higher taxes on people like them, you know one of two things: either the President is in Hollywood, or something interesting is happening in the country at large. In this case, it’s the latter. After three decades in which rising inequality was largely ignored, it has finally emerged as a serious political issue—or, at least, President Obama is trying to turn it into one.

I’ll have more to say later about the “Buffett Rule” that Obama has proposed, which would force people who make upwards of a million dollars a year to pay at least thirty per cent of their income to the federal government. But before getting into a policy discussion, I thought it might be useful to provide a reminder, with the aid of some charts, about the basic facts underlying the debate. As I said, rising inequality is hardly new. One of the first articles I published in the magazine, in October, 1995, was entitled “Who Killed the Middle Class?” It contained a chart I called “The Picket Fence and the Staircase.”

The bar chart on the left shows how during the so-called “Golden Era” of 1947-1973, the inflation-adjusted incomes of the rich, the poor, and the middle class grew in a pretty similar manner—hence, it looks a bit like a picket fence. The bar chart for the period from 1973 to 1993 looks more like a staircase. During that time, the incomes of households in the bottom forty per cent of the income distribution actually fell, the middle stagnated, and upper-income households gained, but not as much as they had during the Golden Era. (I wasn’t the first to use the picket-fence metaphor. I got the idea from Paul Krugman.)

At that stage, it really did look like the rich were getting richer and the poor were getting poorer. Since the early nineteen-nineties, incomes at the bottom of the distribution have grown a bit, but not by much. Depending on which years you select, you can make the chart look a little different, but however you dice the numbers, the basic staircase pattern remains. Households in the upper parts of the distribution have seen their incomes grow a lot faster than poor and middle-income households. Chart 2, which covers the period from 1979 to 2007, shows this clearly.

I took this chart (and the ones that follow) from this year’s Economic Report of the President, which the White House Council of Economic Advisers published in February. It also illustrates another interesting trend—one that bears directly on the debate about the Buffett Rule. At the very highest reaches of the income distribution—the top one per cent of households—incomes have skyrocketed. Between 1979 and 2007, the one per cent saw their incomes rise about eight times as much as those of middle-class households. But they also did a heck of a lot better than other well-to-do households that didn’t quite make it into the top one per cent. Look at the right side of the chart. While the step up from the fourth tier to the fifth is pretty modest, the step up to the one per cent is huge.

Another way to parse the data is to look at the share of over-all pre-tax income that each group receives. The pioneers in this area of research are Thomas Piketty, of the Paris School of Economics, and Emannuel Saez, of Berkeley, whose work is based on an analysis of income-tax filings. Chart 3 reproduces some of their figures.