There are any number of other state and/or Federal laws that prohibit the disclosure of financial records -- regardless of whether the person whose records are disclosed is a "public person" or not.
I agree with you. I pointed this out in response to the comment about this issue falling within the purview of the Times v. Sullivan case.
My point was that disclosing the tax return would not be libelous per se. It might challenge some state shield laws but it’s not libelous.
However, if Madcow falsely reported what was in those returns in order to hurt the President, that would put the Times v. Sullivan case to the test.