Since he won't release his tax returns, and does admit they'd be politically damaging, all we can do is guess. This diary is one in a series of speculative diaries wondering what could possibly be worth the price he is paying by remaining secretive.
Today's idea: He's been audited repeatedly, and had to pay the IRS fines more than once. We know when he was on the board and in charge of taxes for Marriott corporation they wound up paying back taxes several times; we also know that in the one partial return he has released (2010) he went right up to the limit per some sources ... and that's a form he planned on releasing.
So, suppose that an examination of Romney's back taxes reveals having to settle with the IRS after an audit.
Twice? A couple of days worth of news.
Three? Pattern of behavior.
More than three? A persistent issue throughout the rest of the campaign - Mitt Romney, tax dodger.
And based on what we do know, I'm betting on more than three.
Other diaries in the series.
Lots of bad investments
Partnerships with bad people
How he got $100M in his IRA
He didn't tithe
Nothing, he's just pathologically secretive
Hiding stuff from Ann Romney
Rich people write-offs
Church contributions exceed taxes