President Trump vigorously defended his pardon of former Sheriff Joe Arpaio at a Monday press conference, pointing to controversial grants of clemency by his predecessors.

"I assumed someone would ask me the question," Trump said, before launching into a list of examples.

"President Clinton pardoned Marc Rich who was charged with crimes going back decades," Trump said. "He was pardoned after his wife donated hundreds of thousands of dollars to the Clintons."

Trump highlighted Clinton shortening the sentences of "dangerous criminals" such as Weather Underground bomber Susan Rosenberg and "drug dealers" such as cocaine trafficker Carlos Vignali.

He continued: "You've heard the word leaker. President Obama commuted the sentence of Chelsea Manning, who leaked countless sensitive and classified documents to WikiLeaks, perhaps and others. But horrible, horrible thing that he did, commuted the sentence and perhaps pardoned."

Obama shortened Manning's prison sentence, allowing the former private first class to leave Fort Leavenworth after seven years behind bars. Manning, who was not pardoned, had been sentenced to 35 years.

Trump also mentioned Obama's commutation of Puerto Rican independence campaigner Oscar López Rivera's prison sentence for his role in a 1970s bombing campaign.

By comparison, Trump said, "Sheriff Joe is a patriot. Sheriff Joe loves our country. Sheriff Joe protected our borders. And Sheriff Joe was very unfairly treated by the Obama administration."

Arpaio was convicted of contempt last month for defying a judge's order that his department not arrest suspected illegal immigrants without suspicion that they committed a state crime. He faced a maximum six months in prison.

The former sheriff, 85 years old, told the Washington Examiner on Monday that he is considering another campaign for political office.