The order appointing me special counsel authorized us to investigate actions that could obstruct the investigation. We conducted that investigation, and we kept the office of the acting attorney general apprised of the progress of our work. And as set forth in the report, after that investigation, if we had had confidence that the president clearly did not commit a crime, we would have said so. We did not, however, make a determination as to whether the president did commit a crime.Robert Mueller via the New York Times
This was a not too subtle hint to the US Congress that the next action that needs to be taken is by them. Like it or not, they have to impeach Donald Trump or they will be abandoning the framework that this country was founded upon. It is one way or the other, and there is no way in between.
Trump is a criminal, many times over. This was true even before he became the president, as documented over and over on this blog, referencing dozens of news outlets. Now he has committed other crimes that Bobby three sticks cannot charge him for. Congress must take up this task, or admit that they have no power to curb a modern president. If they admit this, they admit that they are no longer a co-equal branch of government.