Nancy Pelosi and William Barr.

Michael McGough, Tribune News Service

The announcement that former special counsel Robert S. Mueller III will testify before two House committees next month is significant only if Mueller goes back on his word. You›ll remember that, in a public statement in May, the former FBI director who investigated possible ties between Russia and Donald Trump›s campaign made clear that he had no desire to testify before Congress. If he were to appear, he added, “I would not provide information beyond that which is already public.”

“If” has become “when.” On Tuesday it was announced that, in response to subpoenas from House Democrats, Mueller would testify on July 17 before that chamber›s Intelligence and Judiciary committees.

It›s important that Mueller reconsider his insistence that the 448-page report he filed with the Justice Department “is my testimony.” He needs to say more, but not for the reason some critics of President Donald Trump are eagerly awaiting his appearance.

Their hope, and that of some of the Democrats who will question the former special counsel, is that Mueller will use his testimony — which is expected to be televised live — to accentuate the findings in his report that make Trump look bad.

And that may happen. Many Americans who didn›t read Mueller›s report were probably surprised to hear what he said on camera about the possibility that Trump had obstructed justice. Mueller explained that “if we had had confidence that the president clearly did not commit a crime, we would have said so. We did not, however, make a determination as to whether the president did commit a crime.” Even if Mueller repeated those words in congressional testimony, it would probably increase the number of Americans who know about that non-exoneration.

If Mueller added even a little rhetorical Hamburger Helper, the effect could be more damaging to the president. Democrats who are skittish about impeachment might abandon their ambivalence.

But paving the way for impeachment isn›t the principal reason Congress and the country need to hear more from the former special counsel. There are ambiguities in Mueller›s statements about obstruction that he needs to clear up.

As the Los Angeles Times observed in a May 29 editorial, the Mueller report “left unanswered questions, most notably whether Mueller would have accused Trump of obstruction of justice if the Justice Department hadn›t decided that a sitting president couldn›t be indicted. The report mentioned that long-standing policy, but it left unclear whether Mueller believed that, in the absence of such a directive, he would have concluded that Trump committed a crime.”

Congress and the country have a legitimate interest in knowing the answer to that question. It›s especially appropriate for Mueller to weigh in now because, after he filed his report, Attorney General William Barr and former Deputy Attorney General Rod Rosenstein concluded on their own that “the evidence developed during the special counsel›s investigation is not sufficient to establish that the president committed an obstruction-of-justice offense.”

To put it another way, Mueller›s superiors overruled his assertion that he was constrained by Justice Department policy from announcing a clear conclusion on the obstruction issue. That should free his tongue.

Yes, such a clarification would be helpful to Congress in assessing whether to open an impeachment inquiry, but it›s not necessary. The House is free on its own authority to decide whether the conduct alleged in Mueller›s report — including a finding that Trump directed then-White House Counsel Donald McGahn to have Mueller removed for supposed “conflicts of interest” — is credible evidence of “high crimes and misdemeanors.” The House doesn›t need an affirmation by Mueller that Trump obstructed justice — except perhaps as political cover.

So one question is whether Mueller is ready for his close-up; the other is whether Democrats in the House (including Speaker Nancy Pelosi, who is cautious about impeachment) are ready for theirs.