Starting with this letter, the additional documents Mueller has requested from the DOJ will allow a complete reconstruction of the process by which Trump went from this ...

The letter, drafted in May, was met with opposition from Donald F. McGahn II, the White House counsel, who believed that its angry, meandering tone was problematic, according to interviews with a dozen administration officials and others briefed on the matter. Among Mr. McGahn’s concerns were references to private conversations the president had with Mr. Comey, including times when the F.B.I. director told Mr. Trump he was not under investigation in the F.B.I.’s continuing Russia inquiry.

To this, the Rod Rosenstein-drafted letter that blames Comey’s dismissal on …

… the Director ignored another longstanding principle: we do not hold press conferences to release derogatory information about the subject of a declined criminal investigation. Derogatory information sometimes is disclosed in the course of criminal investigations and prosecutions, but we never release it gratuitously. The Director laid out his version of the facts for the news media as if it were a closing argument, but without a trial. It is a textbook example of what federal prosecutors and agents are taught not to do.

Trump progressed from a letter that said he was canning Comey because he refused to drop the Russia investigation, to one that said Comey had to go because he was too mean to Hillary.

Now Mueller is collecting all the details on how that transition was made. It’s also clear that Mueller’s team has been going after details of Trump’s Air Force One memo dismissing the meeting between Donald Trump Jr. and the leadership of Trump’s campaign with Russian representatives there to talk about trading “dirt” on Hillary Clinton in exchange for promises about addressing sanctions.

The active pursuit of two different aspects of an obstruction case, both of which directly involve Donald Trump, make the idea that Trump is about to be handed a “not a target” note extremely unlikely.