In this election season, we're hearing a lot of numbers. 9.6 - that's the percentage of Americans who are unemployed. 1.3 trillion - that's the number of dollars in this year's projected budget deficit.
Here's another number, one the candidates don't talk about so much: 80 - out of every $100 that the nation's collective income increased between 1980 and 2005, $80 went to the people who needed it least, the richest 1 percent.
U.S. incomes have been growing more unequal for three decades. The Princeton economist Paul Krugman has labeled this 31-year trend the Great Divergence.
Why aren't politicians talking much about the Great Divergence?
Republicans don't want to talk about it because most of it happened on their watch.
Larry Bartels, a Princeton political scientist, has calculated income trends going all the way back to 1948.
Under Democratic presidents, the biggest gains went to those at the bottom.
Under Republican presidents, the biggest gains went to those at the top.
Bartels found this distinction started to break down when you got to the richest five percent. These high-income Americans did about as well under Democrats as under Republicans.
That may help explain why Democrats don't talk much about the Great Divergence.
Democrats may also worry that complaining about the Great Divergence would make them sound like left-wing class warriors. But there's a conservative reason to object to this trend:
It ain't how things used to be!
Between 1929 and 1973, U.S. incomes didn't become less equal, they became MORE equal. There remained inequalities, to be sure - blacks, women, and various ethnic groups were treated poorly. But otherwise, the 1950s and 1960s were a pretty sweet time to inhabit America's middle class. The economy boomed, and most everybody shared in the prosperity.
We can't turn back the clock. But let's at least recognize that fate did not decree that rich people should gobble up nearly all this past generation's income growth.
As Election Day grows near, the unemployment rate and the deficit still matter a lot.
But the Great Divergence may matter even more.