Romney needs to answer that he will open his book if Obama will open his first.
Considering that Romney's got nothing to hide, and that he plans on being as open with his life's record as most every other modern president, it's better strategy for him to answer Obama's challenge, then demand that he do likewise.
The silence, hems and haws, and obfuscation from the Obama camp will be devastating.
From that point forward, the Romney camp needs to remind the nation at every opportunity that they're still waiting for Obama to reciprocate by releasing his own records.
You know that Obama CAN'T do that, so he'll look like a complete and utter criminal before the American people.
This is a perfect political trap. Obama set it, then promptly stepped right into it. It's up to Romney to spring it now.