The IRS stipulates that the individual tax returns for the president and the vice president are subject to mandatory examinations. The policy has been in place since the Watergate scandal meaning that every president since Richard Nixon has had their income tax returns audited.
The IRS handbook stipulates in detail how these audits are performed. Specific personnel are assigned to the audit, and the agency works with representatives for the president and vice president during the review. Personnel are even required to keep the returns locked in a secure drawer and kept in an orange folder.
#6 the IRS must have missed all the bribe money the obamas and Biden were getting.