From the moment that Robert S. Mueller III was appointed to serve as special counsel in the investigation into possible collusion between Donald Trump’s campaign and Russia, there was an asterisk.

Mueller’s appointment was intended to offer some protection to the investigation, which, when it began in May 2017, seemed as though it might be at risk from a president who’d just ousted the director of the FBI. Deputy Attorney General Rod J. Rosenstein reportedly made the appointment (after then-Attorney General Jeff Sessions’s recusal on Russia-related matters) in part out of concern that Trump would interfere further. A special counsel would remove the investigation from Trump’s grasp.

But only partially. Under the regulation establishing Mueller’s role, the Justice Department would serve as a backstop.

“The Special Counsel shall not be subject to the day-to-day supervision of any official of the Department,” the regulations say. “However, the Attorney General may request that the Special Counsel provide an explanation for any investigative or prosecutorial step, and may after review conclude that the action is so inappropriate or unwarranted under established Departmental practices that it should not be pursued.”

For most of Mueller’s tenure, that meant that Rosenstein could tell Mueller what investigations or prosecutions he could and couldn’t pursue. Once Sessions was fired after the 2018 midterm elections and his replacement confirmed, that ability fell to Barr.

In other words, if Mueller wanted to launch an investigation into, say, Ivanka Trump, Rosenstein or Barr could have asked why and then, if desired, kept him from doing so. That meant that for close Mueller watchers, there was always a factor of the unknown: Was Mueller homing in on Donald Trump Jr. (as Trump Jr. at one point seemed to believe), only to have the Justice Department protect him?

This was especially interesting as an idea because of another part of the special counsel’s regulations. Mueller’s final report, delivered to Barr on Friday, doesn’t automatically become part of the public record. Instead, according to the regulations, Barr had only to inform Congress when Mueller’s work was completed — and provide “a description and explanation of instances (if any) in which the Attorney General concluded that a proposed action by a Special Counsel was so inappropriate or unwarranted under established Departmental practices that it should not be pursued."

In other words, if Barr or Rosenstein had blocked an investigation into Trump Jr., the Justice Department would have to tell Congress. That would open up a whole raft of possibilities for Democratic leaders in the House who are champing at the bit to uncover whatever rocks they can — or for prosecutors in other jurisdictions, such as New York state, looking to make a name by targeting Trump’s inner circle.

Late Friday afternoon, Barr’s message to Congress was sent. And one line in it answers the question about Trump Jr. or any other truncated investigations succinctly.

Barr noted the above requirement about instances in which Mueller was blocked from pursuing an investigation.

“There were no such instances during the Special Counsel’s investigation,” he then wrote. In other words, no low-hanging fruit waiting to be picked.

That does not necessarily mean that Mueller’s work will not lead to any further prosecutions. The New York Times reports that “some aspects of his inquiry remain active” and may return to the Justice Department with prosecutors released from duty on the special counsel’s team.

There was also the possibility that Mueller obtained some indictments that remain under seal. ABC News considered this question in November, citing experts who noted that the number and duration of the sealed indictments that have been filed in the D.C. district — where Mueller’s grand jury was empaneled — were unusual. However, NBC’s Tom Winter reports that there are no further Mueller-led indictments under seal.

It’s likely, then, that the indictments already obtained by Mueller may constitute the entirety of his work. Given the slow release of new charges and documents, we can lose sight of how much Mueller and his team actually compiled — hundreds of pages of indictments or guilty pleas from dozens of people on scores of charges. (That work is outlined in the graphic below.)

With the letter sent Friday, everything that Barr was mandated to report to Congress has been transmitted. For those still worried about coming into Mueller’s crosshairs? Barr’s confirmation that the Justice Department didn’t intervene to halt any possibly fruitful lines of inquiry will no doubt come as a relief.