The Obama campaign is calling on Mitt Romney to release five years of his tax returns, and it promises it will end its criticism on the issue if Romney does so.

The latest chapter in the tax battle came in a letter from Obama campaign manger Jim Messina, who made the offer.

"Gov. Romney apparently fears that the more he offers, the more our campaign will demand that he provide," Messina wrote. "So I am prepared to provide assurances on just that point: if the governor will release five years of returns, I commit in turn that we will not criticize him for not releasing more--neither in ads nor in other public communications or commentary for the rest of the campaign."