America's growing inequality is likely to play an important role in this election - and rightly so. Americans see that something is happening to our society: We have become increasingly divided. We may all be in the same boat - but some are traveling steerage and others first class.

Inequality is now far higher than just 30 years ago. The top 1 percent today gets around 20 percent of the nation's income - twice what it did two decades ago. The top 0.1 percent's share has almost tripled. Disparities in wealth are even greater.

Some on the right argue that this is the politics of envy. They say what matters is not the share of the pie - but the size of the slice. But inequality, especially of the U.S. variety, is bad for growth. The country grew faster in the decades after World War II - when it was also growing together, with all groups seeing increases in income. But those at the bottom were growing the most.

By comparison, growth since 1980 has been slower, as the share of the bottom and middle has diminished. That means that those in the middle, ordinary Americans who work for a living, let alone those at the bottom, are getting a smaller slice of a pie that is smaller than if we had continued growing as we did postwar. The net result is disheartening: Most Americans are worse off today than they were 15 years ago.

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