Let's backtrack a bit. When President Donald Trump pardoned Arpaio in August, he nullified any future punishments the former lawman might face from his conviction. Trump's pardon was unusual; most presidential pardons come after sentencing.
Presidential pardons can give a convicted criminal back their freedom, voting rights and right to bear arms. But a pardon doesn't give the person a clean slate, since their original offense stays on the books.
But a clean slate is exactly what Arpaio wants: He asked the judge to vacate all findings in the case, which would clear his name of any wrongdoing.
The judge dismissed the case against Arpaio with prejudice, meaning it can't be brought back to court. But she took Arpaio's request to wipe away all rulings in the case under advisement, meaning she has yet to make her decision.
There's a reason Arpaio's pardon drew so much attention and scrutiny. Trump's power to pardon could play a key role in special counsel Robert Mueller's investigation into Russian interference in the 2016 election.
It's been reported Mueller's team is researching what — if any — limits exist on the commander-in-chief's clemency.
Trump hasn't said whether he'll pardon any of his associates caught up in the Russia probe. But even the idea of a pardon could keep some witnesses from cooperating with Mueller's investigation, since they wouldn't have to worry about punishments.