We propose a 2% annual wealth tax on households owning more than $7.2 million in net assets. Such a tax would target the 0.5% of Americans at the top of the pyramid, and would yield at least $70 billion a year. This calculation is based on Federal Reserve data that we have updated to take into account the recession’s impact on housing and stock prices to 2009. Because we have used very conservative assumptions, the revenue yield could well be higher.

Obama’s operational proposal for a “Buffett tax” is vague, so it’s hard to predict how much it would raise. But our initiative would generate at least half the $1.5 trillion in deficit reduction that Congress’ super-committee is aiming to achieve over the next decade. And the burden would fall on the Americans who have suffered least from the economic downturn.

There is more at stake than fairness. Our proposal would address a deeper issue. There comes a point at which extreme wealth concentration threatens the very existence of democracy, and we are reaching that point.

This is one of the tragic lessons of Latin American history, where democracy has repeatedly bumped up against tight economic oligarchies that feel threatened by majority rule.