Paul Manafort, President Trump's former campaign chairman, leaves federal court in Washington on April 4. (Andrew Harnik/AP)

Two developments this week shed light on where special counsel Robert S. Mueller III’s investigation might be heading. What grabbed most of the headlines was the news that prosecutors informed President Trump’s lawyers that he is currently a subject, not a target, of Mueller’s inquiry. Less noticed, but perhaps more significant, were revelations in a filing by prosecutors in the case against former Trump campaign chairman Paul Manafort.

Manafort had moved to dismiss his indictment, claiming that Mueller exceeded his authority by investigating financial crimes unrelated to the 2016 presidential campaign. In response, prosecutors disclosed a heavily redacted memo from last August in which then-acting attorney general Rod J. Rosenstein detailed the scope of Mueller’s investigation. That memo specifically authorized the special counsel to investigate not only possible crimes arising out of payments Manafort received during his activities in Ukraine before the campaign — in other words, activities that form the core of the indictments later brought against him — but also possible collusion by Manafort with Russians during the election.

We knew, of course, that a possible conspiracy with Russians to influence the campaign was at the center of Mueller’s probe. But the memo specifically authorizes a focus on collusion by the former campaign chairman himself. The investigation of Russian ties within the campaign clearly is not limited to more-fringe players such as George Papadopoulos or the ever-surprising Carter Page. The Rosenstein memo means the FBI had a basis to suspect Russian collusion involving the very highest levels of the Trump campaign.

The filing also answered critics who claimed Mueller had “gone rogue” by prosecuting crimes that had nothing to do with the election. It’s now clear the special counsel has been doing things by the book. It makes perfect sense to investigate Manafort’s other financial entanglements. Doing so could identify points of leverage Russians had over Manafort or relationships that could have facilitated any collusion involving the campaign.

The final tantalizing aspect of Rosenstein’s memo is how much we can’t see. The disclosed authorizations concerning the investigation of Manafort take up perhaps one-fifth of the memo. The rest is blocked out. That’s a lot of additional allegations that Mueller is authorized to investigate — and we probably still don’t know what all of them are. There could be multiple shoes yet to drop.

It’s less clear what to make of the news about Trump’s status in the investigation. A target is someone prosecutors view as a likely criminal defendant, while a subject is someone whose conduct is within the scope of the investigation but who is not currently considered likely to face charges. It was already clear that Mueller was investigating Trump’s conduct, so it’s really not surprising that he would be at least a subject.

Trump and his attorneys may be justifiably heartened by the fact that he is not currently a target. But this is not a typical case. For one thing, Mueller may consider himself bound by opinions from the Justice Department’s Office of Legal Counsel concluding that a sitting president cannot be prosecuted. Under that policy, one could argue Trump could never be a target, because charging him is not an option. In that case, Trump being told he is merely a subject may not actually say much about how prosecutors view his actions — or how those actions will be characterized if Mueller prepares a report instead of an indictment.

More broadly, it’s not unusual for subjects to morph into targets as an investigation proceeds. A subject who agrees to an interview can also become a target based on the interview itself if he makes false statements or inadvertently leads prosecutors to other misconduct. If Trump were to walk into an interview thinking he now has nothing to fear, his status could change quickly.

A final wrinkle: Under Justice Department policy (which Mueller is bound to follow) prosecutors generally will not subpoena targets to the grand jury. But if the president is merely a subject, Mueller has the option of subpoenaing him if he refuses an interview. Trump’s status as a subject could lead to a possible showdown over a grand jury appearance — which would be very dangerous ground for the president.

There have been no indictments of campaign officials for conspiring with Russians to influence the election, and we don’t know whether any are coming. We don’t know whether Trump will agree to be interviewed, although I still believe that’s unlikely. We don’t know how Mueller will resolve the questions about the president’s own conduct, and what form his final product will take. The developments this week have dropped a few more puzzle pieces into place — but the full picture remains far from clear.