Anonymous wrote:OP again. Good answers so far. I am genuinely interested in this. Obviously, there is a pretty good chance that not releasing his tax returns might be political suicide, so the contents must be absolutely toxic.
Here's some of the speculation, assuming that Romney is on the up and up about his 13% federal income tax rate (compared to 20% for Ryan and the mid-20s for the Obamas):
1. Lots of dodgy (though perhaps legal) tax avoidance structures, using an array of offshore havens. Remember that Romney has only released 2010, when he had actively been running for president for 4 or 5 years. These structures take a while to clean up, and look at the outrage and derision Mitt met with his 2010 return. The earlier ones are probably much more problematic.
2. Mitt's returns contain other politically toxic items. Some believe that Mitt made a big bet against the subprime market and profited very handsomely. Not illegal at all and perhaps smart investing, but political poison while other Americans were losing their jobs, savings and homes during the financial crisis.
3. More clarity on how the aforementioned 401k somehow grew to a gazillion dollars. Speculation is that Mitt put investment shares into them using valuations that tax professionals euphemistically call "extremely agressive."