Robert Mueller’s effort to stand outside partisan politics in his investigation of President Donald Trump will no doubt follow him into the pages of American history. But for now there are still some questions that he needs to answer, despite his reluctance to say anything more than is contained in his 448-page report.

Unfortunately, it’s far from clear that members of the House Intelligence and Judiciary committees will ask the right questions when Mueller testifies before them, under subpoena, on July 17. With so much attention focused on the hearing, congress members from both parties won’t be able to resist wasting the public’s time on self-justifying statements rather than questions.

Mueller has essentially left it to Congress to determine whether Trump violated the law by obstructing justice, and if so, whether the president’s conduct was so egregious that it warrants impeachment. But he needs to explain, more clearly than his report does, why Trump would want to block an investigation into whether he or others in his campaign criminally conspired with Russian authorities in their effort to influence the 2016 presidential campaign. After all, Mueller found that no Americans entered into that conspiracy: AKA “no collusion.”

As Attorney General William Barr said in his much-criticized four-page summary of Mueller’s findings, “while not determinative, the absence of such evidence bears upon the President’s intent with respect to obstruction.” That is, one of the essential elements of a crime would have to be that Trump acted with corrupt intent, for example, in dismissing James Comey as FBI director.

That’s what Mueller needs to explain to Congress. He might be asked to turn to the section starting in the last paragraph of Volume II, page 76 of his report:

The evidence does not establish that the termination of Comey was designed to cover up a conspiracy between the Trump Campaign and Russia: As described in Volume I, the evidence uncovered in the investigation did not establish that the President or those close to him were involved in the charged Russian computer-hacking or active-measure conspiracies, or that the President otherwise had an unlawful relationship with any Russian official. But the evidence does indicate that a thorough FBI investigation would uncover facts about the campaign and the President personally that the President could have understood to be crimes or that would give rise to personal and political concerns. Although the President publicly stated during and after the election that he had no connection to Russia, the Trump Organization, through Michael Cohen, was pursuing the proposed Trump Tower Moscow project through June 2016 and candidate Trump was repeatedly briefed on the progress of those efforts. In addition, some witnesses said that Trump was aware that ■■■■ REDACTED: ONGOING MATTER ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■ at a time when public reports stated that Russian intelligence officials were behind the hacks, and that Trump privately sought information about future WikiLeaks releases.

That one passage raises many questions. What “facts about the campaign and the President personally” is the report referring to? Were those facts uncovered in “a thorough FBI investigation”? And of course, what about the redaction Barr made to the report in a passage that starts with some witnesses saying Trump “was aware that” and ends with “Trump privately sought information about future Wikileaks releases”? Walter Shapiro wrote in the New Republic that it’s “the legalistic equivalent of the cavalry riding over the hill to save Trump in the last reel of an old Western.” Is it? For a start: Does Mueller regard this redaction as a necessary one? What is the “ongoing matter?” (The language corresponds with a passage in the obstruction-of-justice indictment of Trump friend Roger Stone: “On multiple occasions, Stone told senior Trump Campaign officials about materials possessed by Organization 1 [Wikileaks] and the timing of future releases.”)

Those are a few of the questions raised by just a page or two of Mueller’s report. And for all Mueller has done for his country by conducting a careful investigation under extraordinary pressure, it’s necessary to ask him to do a little more.