We called it. Robert Mueller has announced that he is teaming up with Eric Schneiderman, the NYS attorney general. Right now the cooperation is about Manafort but we expect future announcements.
As we pointed out, President Trump can only pardon people for federal offenses. So if Mueller finds evidence of violations of New York laws, Schneiderman and he can threaten the perpetrators with state prosecution unless they cough up more evidence.
A related question: can it really be true that Arpaio has broken no state laws? I know there have been multiple civil suits; did he comply with all of them?