The latest development in the Paul Manafort case is a big deal

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.

.. a subject is someone whose conduct is within the scope of the investigation but who is not currently considered likely to face charges.

.. 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.

.. 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.

.. 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.