To commemorate the event, the political website FiveThirtyEight published a comprehensive and deeply sourced article (link here) comparing the success of Mueller's investigation with other recent criminal investigations targeting White House senior officials.
The bottom line: Mueller has been more successful than any other such criminal investigation, with the exception of Watergate, based on the number of individuals charged with criminal offenses.
The article also makes clear that predicting how long Mueller's investigation will run as well as the outcome, something the White House has done repeatedly, is nothing short of foolish.
It could be another Watergate, which ended a presidency. It could be another Iran-Contra, which did not directly entangle a President but tarnished his legacy forever and exposed his increasingly frail state. Or it could be another Whitewater, which kept building in steam until it triggered a President's impeachment.
Mueller's team has kept a tight lid on what exactly is happening and it's rare that any details emerge and that almost exclusively comes from people the prosecutors have already met and, in some instances, subpoenaes. Just yesterday, for instance, it was revealed that Mueller had indicted someone back in January and then "flipped" him to testify against Trump's former, now-indicted campaign chairman.
That's why we all need to stay tuned and pay attention.