The Testosterone Pit (not a name I would have chosen) has an article out this week that shows in just one graph what the US problem with corporate tax receipts is:
The source is Ralph Dillon at Global Link Data.
That's also a clear indication of where a major source of the inequality problem comes from. The graph starts in 1947 and runs to 2012 (it is a bit hard to read that) and the blue line is US corporate profits and the red line federal corporate taxes. Tax havens, lobbying and tax avoidance fuelled the gap: we pay the price in economic stagnation.