The former Arizona sheriff had become infamous for running Tent City, known for its harsh conditions and being what Arpaio himself referred to as “a concentration camp.” The resources put into detaining immigrants also sapped county resources, leading to a backlog of various other violent crimes.

Arpaio was convicted of contempt for violating a judge’s order preventing him from detaining immigrants based on racial profiling and their legal status. Though he was unlikely to serve any jail time, Trump issued a pardon. The pardon was controversial in how it eschewed tradition, including any layers of review or even a formal application by Arpaio.

Arpaio later ran for US Senate, but lost the primary. In an interview during his campaign, he seemed to be unaware that acceptance of a pardon is tantamount to an admission of guilt, per the US Supreme Court finding in Burdick v. United States.

USA Today – Analysis: Trump’s bold Joe Arpaio pardon breaks with presidential tradition
The New York Times – Trump Pardons Joe Arpaio, Who Became Face of Crackdown on Illegal Immigration
NPR – Arizona Sheriff Joe Arpaio Under Fire For Mishandled Sex-Crime Cases
Wikipedia – Burdick v. United States
Wikipedia – Pardon of Joe Arpaio
Wikipedia – Joe Arpaio