Now that Robert Mueller has agreed to testify before Congress, some commentators are rushing to declare that “expectations” could be dashed. And some Democrats are also downplaying expectations, apparently fearing they will fail to produce a dramatic breakthrough moment.

But there is a way that House Democrats can use Mueller’s testimony to expose an important and somewhat overlooked aspect of Trump’s misconduct and, crucially, its consequences as well.

Handled correctly, this could shine further light on one of Trump’s biggest crimes — by which I mean moral crimes: The degree to which Trump’s obstructive conduct actually did frustrate an investigation into a foreign attack on our political system, and how he obscured his own eagerness to work with Russia in spite of it, in various nefarious ways.

The former special counsel will appear in open sessions before the Judiciary and Intelligence committees on July 17th. Mueller has already telegraphed resistance: In his recent public remarks, he vowed that if he appears before Congress, he will “not provide information beyond that which is already public.”

Still, there is at least one angle that could prove fruitful. Former federal prosecutor Barbara McQuade outlined a detailed case that Mueller’s report shows that efforts to obstruct the investigation by Trump and his associates might have actually worked, by limiting what Mueller’s investigation was able to establish about efforts to conspire with Russia.

Democrats can use the Mueller testimony to pull on this thread in a variety of areas:

1. Trump’s negotiations over a Trump Tower Moscow. Rep. Adam Schiff, D-Calif., the chairman of the House Intelligence Committee, tells me that Democrats will ask Mueller expansive questions about Trump’s negotiations over the real estate project in Moscow, which continued through the 2016 GOP primaries, something he and former fixer Michael Cohen lied to conceal.

Mueller’s report says little about the counterintelligence dimension to the investigation, as opposed to the criminal one. House Democrats are only just getting briefed on the former now.

Schiff tells me that asking Mueller about the negotiations with Russia over Trump Tower Moscow in a counterintelligence context could be revealing: Though no crimes were committed, investigators might have worried that those talks were nonetheless compromising.

“The fact that the president was denying business dealings and at the same time seeking the Kremlin’s help to make that deal happen - when it was discovered, the Kremlin tried to help the president cover it up,” Schiff says. “Those are issues that are not fully fleshed out in the report.”

Schiff tells me that beyond whether criminality occurred, another big question is whether there were “conflicts of interest” that “resulted in U.S. policy favoring Russia against the interests of the American people.” Remember, Trump repeatedly exonerated Russian leader Vladimir Putin on the campaign trail while pursuing those private dealings.

Democrats can also ask Mueller about efforts to cover up that whole story. Cohen testified falsely to Congress about the Moscow deal’s timeline, and that testimony circulated among Trump’s lawyers. Schiff tells me that Mueller can be asked “how much they looked into others who were involved in Cohen’s false testimony,” and whether investigative difficulties ultimately prevented a definitive conclusion on that.

2. Trump’s refusal to sit for an interview. Mueller’s report explicitly states that the special counsel informed Trump’s lawyers that an interview was “vital” and in the public interest. Trump submitted written answers instead. But Mueller’s report says Trump claimed more than 30 times that he did not remember the information he was being asked about, which demonstrated the “inadequacy of the written format.”

Democrats can probe Mueller about this. “What were you unable to get that you were hoping to get, as a result of his refusal to cooperate?” McQuade tells me Democrats can ask Mueller. “What were some of the questions you were unable to answer?”

3. The Trump Tower meeting and Donald Trump Jr.’s refusal to be interviewed. The Mueller report states that Trump Jr. “declined to be voluntarily interviewed” by Mueller, who wanted to ask him in particular about the infamous Trump Tower meeting.

As Benjamin Wittes notes, this suggests Trump Jr. may have asserted his Fifth Amendment right to avoid self-incrimination, and that as a result, Mueller may have been unsatisfied about what he could learn about Trump Jr.’s participation in the meeting.

Democrats can ask Mueller about this. Trump Jr. took this meeting in the full expectation that he’d receive dirt on Hillary Clinton from the Russian government. As McQuade points out to me, if participants like Trump Jr. were questioned, Mueller might have been able to determine if they “willfully” took this meeting while knowing of the legal and ethical issues it raised.

Mueller could clarify that Trump Jr.’s refusal to testify impeded efforts to learn that — which would make both the meeting and that refusal to testify look more serious.

Democrats can also ask Mueller if Trump Jr. did indeed plead the Fifth. This requires caution, since doing that isn’t necessarily a sign of guilt, McQuade notes, but it might undercut Trumpworld’s spin that they were all “cooperative” with the investigation.

4. Other contacts between Trump’s people and Russia. The Mueller report established extensive connections between various Trumpworld figures and Russia that constituted efforts to conspire with Russian electoral sabotage. But the report also notes that some officials “affiliated with the Trump campaign lied” to investigators, which “materially impaired the investigation.”

McQuade tells me Democrats can ask Mueller: “What were the questions about links to Russia that you were unable to answer as a result of these obstructive acts?”

The big picture here: Trump didn’t merely commit extensive and likely criminal obstructive acts to protect himself from scrutiny. He also obstructed an investigation into a foreign effort to sabotage our electoral process. Trump also eagerly encouraged and sought to profit off that interference, and even sought profitable dealings with Russia, both of which he and his top associates concealed from the public.

Mueller can shed light on this larger tale of wrongdoing.

Greg Sargent is a columnist with The Washington Post.