Federal tax law should require the IRS to immediately begin publishing the tax returns of anyone registered as a Federal candidate with the FEC or in Federal office. Published returns should cover five years prior to candidacy and five years after holding office.
The IRS must publish the returns since Congress can't compel individuals to do so themselves. Requiring candidate's action would establish a "qualification" for office not in the Constitution. But, modifying IRS privacy rules wouldn't compel individual action and thus is allowed.