The US Presidential election debate seems pretty much focused on Mitt Romney's tax affairs, in no small art due to the excellent work of  the Tax Justice Network's Nick Shaxson and his first rate article in Vanity Fair.

Now I'm interested in another hypothesis: that the reason why Mitt won't release his tax return for 2009 is that he took advantage of a tax amnesty that year to declare a previously undeclared offshore account.

You can read more about this idea here.

But it's a fascinating idea - and a game changer if true in this debate. Being offshore is one thing. Some people even think that the duty of a wealthy person in the US. But being offshore and undeclared? That's goodbye to the Republican challenge time.

I would be amused.