Shortly after news broke Tuesday night that Robert S. Mueller III would testify in an open hearing on July 17, Democratic Sen. Brian Schatz (Hawaii) tweeted this:

“Robert Mueller will not save us,” Schatz said.

Schatz is probably right. Democrats have long dreamed of Mueller showing up at a hearing and blowing the lid off the entire Russia investigation. That fantasy loomed especially large when it wasn’t clear how much of his report Attorney General William P. Barr would share. And now, even though we have seen the vast majority of it, the conclusions and outcome haven’t match the expectations of many on the left. Enter the former special counsel, answering questions from lawmakers about the matter.

Mueller himself, though, has tempered expectations.

“Any testimony from this office would not go beyond our report,” Mueller said a month ago in his only public comments. “It contains our findings and analysis and the reasons for the decisions we made. We chose those words carefully and the work speaks for itself. And the report is my testimony. I would not provide information beyond that which is already public in any appearance before Congress.”

This very much matches Mueller’s by-the-book reputation, and if past is prologue, Mueller isn’t going to be saying much that he doesn’t want to.

But even if Mueller doesn’t intend to add much to the record July 17, it’s possible the right kind of questioning could draw him out a bit or add clarity to some of the murky issues still on the table. I ran through some of them last month, and there are a few that still apply.

Chief among them is confusion and controversy about how Barr has handled his report. Barr has claimed that Mueller told him that he wouldn’t have accused Trump of obstruction of justice even if the Justice Department didn’t have a policy against indicting a sitting president. Mueller in his statement last month slow-walked any criticisms of Barr, but he also suggested that he wasn’t in the business of making any such determinations. A key question for him is whether Barr was accurate in recounting their private conversations, on this and other matters.

Second would be whether Mueller felt it appropriate for Barr and then-Deputy Attorney General Rod J. Rosenstein to determine that they would not accuse Trump of obstruction. Mueller had explicitly said he couldn’t clear Trump of obstruction, but then Barr and Rosenstein took it a step further. Mueller presumably won’t answer this question directly, but even an evasive answer could say a lot. Maybe he declines to endorse Barr’s and Rosenstein’s decision. Maybe he uses the question to reinforce that he couldn’t clear Trump. Those answers would be telling.

Third is his relationship with Barr. Mueller said he appreciated Barr’s degree of disclosure and that he believed it was handled in “good faith.” But did he think other aspects were handled in good faith? Mueller wrote a letter after Barr released his initial conclusions, clearly unhappy with the perceptions it had created. Given that Mueller is on the record on that, it would seem it’s fair game to ask him to clarify exactly what he was mad about. He could, of course, simply say, “The letter speaks for itself and was meant to be private.”

Fourth, Mueller could provide some clarity on the distinction between collusion and conspiracy. Trump has claimed the report bolstered his long-running “no collusion” talking point, but Mueller explicitly said he wasn’t deciding about the broader concept of collusion — which isn’t in the criminal code — but rather about conspiracy and cooperation. He said neither took place. Mueller isn’t going to come out and say that, yes, Trump and/or his campaign did collude, but he could make clear that it’s an open possibility or reinforce his report’s conclusion that the Trump campaign actively encouraged Russia’s assistance.

And lastly, lawmakers could conceivably draw Mueller out on the evidence for obstruction. As I’ve written, there were five events in which Mueller seemed to find evidence to support the three criteria needed for obstruction charges. Mueller probably won’t say, “Yes, the evidence satisfied the requirements for obstruction charges,” but lawmakers could make him reinforce that evidence existed for each criterion.

As with all of these, if they approach it smartly, they could land some important moments. But that’s hardly a given in congressional hearings. And if Mueller is intent on erecting a stone wall at the witness table, his experience in these settings could make it impenetrable.