When President Donald Trump announced on Friday that he is pardoning former Maricopa County Sheriff Joe Arpaio, who was convicted on July 31 of contempt of court for continuing use immigration-enforcement tactics that had been found by a judge to be discriminatory, he was taking part in a presidential prerogative that dates back to the earliest days of the United States.

But, especially considering reports that the Department of Justice was not fully in the loop about Trump's decision, the announcement represents a departure from the pardon process of the past few decades, in which pardons have followed petitions to the DOJ's Office of the Pardon Attorney. In addition, particularly for more controversial cases, they have tended to come later in presidents' terms.

It remains to be seen how President Trump will use his power to pardon for the rest of his term. But, as the history of that power makes clear, there's one right way to do so, especially in high-profile cases: very carefully.