Fiji, the Tax Man and Joe's Estate

Under "Fiji: Undemocracy in Action", commenter Joe B reminds us that Fiji is a tax haven for many, including the family of the senior senator from Massachusetts.

The Obama administration and some members of Congress would like to begin cracking down on tax havens by giving

... U.S. regulators the authority to take special measures against foreign jurisdictions and financial institutions that impede U.S. tax enforcement.

When certain members of Congress decided to jack up the red herring of bonuses issued to some AIG staff members, they saw no problem with and vociferously advocated for an ex post facto law that would have retroactively taxed those bonuses at a rate of 90%+.

With that "precedent" in mind, if the tax status of Fiji is redefined under law, will Congress then pass an ex post facto law that would recover the many millions in estate taxes lost to trusts, including that of Joseph Kennedy, Sr., domiciled in Fiji rather than the United States?