The self-proclaimed toughest sheriff in America will appear in court Tuesday to testify about his failed corruption investigations against three public officials who claim the cases were trumped up.

Maricopa County Sheriff Joe Arpaio will testify at an ally's attorney discipline hearing at a time when a federal grand jury is investigating abuse-of-power allegations against him and the U.S. Justice Department is conducting a civil rights investigation of his immigration patrols.

The politically powerful sheriff, who is being courted by four Republican presidential hopefuls for his endorsement, will testify at former Maricopa County Attorney Andrew Thomas' attorney discipline hearing.

Arpaio wouldn't face any punishment if Thomas is found to have violated ethical rules, but the hearing could provide the first official comment from the state's legal establishment on whether the investigations were valid.

Lawyers pressing the discipline case said that the officials, judges and attorneys who crossed Arpaio and Thomas in political disputes were often targeted for investigations and, in some cases, were criminally charged.