What Mueller's move means

Why it matters, from MSNBC's Ari Melber: "[W]e're moving away from a political fight, where everyone can see it the way they want, and into ... a legal process — where there are rules of evidence, facts are established. ... Bob Mueller is known to be a pretty careful prosecutor."

Be smart: Matt Miller — former Obama Justice Department official, and close Mueller watcher, emails me: "I think it means this will be a rolling investigation. Rather than conduct his entire investigation and then wrap things up with indictments and possibly a report at the end, he is doing it in stages, the way the Justice Department might attack a drug cartel or a mafia family."

• Miller adds that this "is a watershed moment for the politics surrounding the investigation. In less than six months on the job, Mueller has already returned indictments.

• "This isn't a fishing expedition or a witch hunt — it's an investigation that's already born fruit with a grand jury of regular Americans finding probable cause that a crime was committed."