Lee Drutman, a Senior Fellow at the Sunlight Foundation, compared the tax returns of previous presidents against that of Mitt Romney.
This scatter plot highlights two things: First, the two highest income years we observe are Romney 2011 ($21.6 million) and Romney 2010 ($20.9 million). Nobody else comes close. The next closest are Obama 2009 ($5.5 million) and Obama 2007 ($4.1 million).
Second, the two lowest effective tax rates we observe also belong to Romney. The 2012 Republican candidate paid an effective tax rate of 13.9% in 2010 and 15.4% in 2011. Next lowest is George H.W. Bush, who paid a 15.5% rate in 1991. By contrast, in Obama’s two highest earning years, he paid a rate of 32.6% (2009) and 33.7% (2007).
Of course the difference is there because most of Romney's income comes from investments, but wow, what a contrast.