WASHINGTON — House Democrats hope to boost public support for impeaching President Trump when former special counsel Robert S. Mueller III testifies to Congress for the first time Wednesday about his investigation into Russian interference in the 2016 election and alleged obstruction of justice.

Mueller has warned he doesn’t intend to deliver any bombshells beyond those detailed in the 448-page report released in mid-April. But Democrats hope he will summarize its findings in short, digestible TV soundbites that will spur new outrage, especially among lawmakers on the fence about whether to try to force Trump from office.

For House Democrats already committed to impeachment, Mueller’s back-to-back testimony before the House Judiciary and Intelligence committees may be their last best chance to muster a majority short of dramatic new misconduct by the president — or an about-face by Speaker Nancy Pelosi (D-San Francisco), who has steadfastly opposed impeachment proceedings for now.

Democrats acknowledge that they need a televised moment to counter Trump’s claim of “complete and total exoneration” shortly after Atty. Gen. William Barr gave a public summary of Mueller’s report on March 24.

But Mueller decided that Justice Department rules barred indictment of a sitting president, adding, “While this report does not conclude that the president committed a crime, it also does not exonerate him.”

Democrats hope they can get Mueller to explain what he meant and say whether he agreed with Barr that no obstruction of justice occurred.

“We simply want to bring the report to life, and if Robert Mueller would simply, on live TV, highlight the important parts of the report, that would be very helpful to the American people,” said Rep. Ted Lieu (D-Torrance), who sits on the Judiciary Committee.

“It could” move people on impeachment, said Rep. Raja Krishnamoorthi (D-Ill.), a member of the Intelligence Committee. He hopes Republican members repeat the president’s mantra of “no obstruction, no collusion” often enough to force Mueller to correct the record.

“You don’t know what’s going to happen, but the point is that he is of sufficient stature that I do think it really could change minds depending on what is said,” Krishnamoorthi said.

For now, there is not enough support among House Democrats to pursue impeachment.

On Wednesday, the House voted down articles of impeachment. The majority of Democrats joined Republicans to derail the resolution, overwhelming the 95 Democrats who voted to keep it alive.

Some impeachment supporters considered the vote — forced by Rep. Al Green (D-Texas) — a misstep because it forced rank-and-file Democrats to show their hand before Mueller’s testimony.

But the vote showed more support than expected. More than 80 Democrats, including 17 from California, had voiced support for starting an impeachment inquiry. A total of 218 votes, a simple majority, would be needed to pass articles of impeachment.

But time is relatively tight: Lawmakers will leave Washington for a six-week break days after Mueller testifies.

If he sets off alarm bells, lawmakers could face angry constituents in their districts who favor impeachment.

If the hearing is a dud, the August recess could effectively put an end to the chatter. Congress will be in session only 10 weeks this fall, too little time to organize impeachment proceedings before the 2020 campaign is in full swing.

Some impeachment supporters argue that it’s already too late and that Mueller won’t have an impact.

“I think time is running out,” said Rep. Jackie Speier (D-Hillsborough), who still argues that the Mueller hearing is important to correct the public perception. “It will have the effect of shining a very bright light on a very corrupt organization, the Trump Organization.”

Pelosi and most senior Democratic leaders argue that trying to remove the president without overwhelming evidence, bipartisan support and strong public backing would be fruitless — and perhaps even strengthen Trump’s reelection bid.

Even if the House impeached the president, the Republican-controlled Senate is extremely unlikely to muster the two-thirds majority needed to remove the president from office.

For that reason, and because of Mueller’s well-documented discipline, Democrats sought to lower expectations for Wednesday’s high-profile hearing.

“I do think attitudes have hardened a great deal, so I don’t know that it’s reasonable to expect some epiphany,” said Rep. Adam B. Schiff (D-Burbank), chairman of the Intelligence Committee. “But I do think the American people are entitled to all the information, and this is a powerful way to give it.”

For three hours Wednesday morning, Democrats on the Judiciary Committee will focus on a handful of the episodes Mueller outlined suggesting Trump sought to obstruct justice, including ordering former White House Counsel Don McGahn to fire Mueller, telling former aide Corey Lewandowski to instruct then-Atty. Gen. Jeff Sessions to limit the scope of the investigation, and potential witness tampering.

In the afternoon, Democrats on the Intelligence Committee will focus on Mueller’s conclusion that the Trump campaign welcomed Russian help in the 2016 election but did not assist the Kremlin-backed operation.

Republicans are expected to focus on the parts of the report that cleared Trump of wrongdoing, and push Mueller to justify his hiring of prosecutors whom Trump routinely denounced as “angry Democrats.”

In Capitol Hill meetings, Democrats have tried to set a strategy for Mueller’s appearance, suggesting that they will try to pace their questions to let him speak and not step on one another’s topics — both of which often happen in congressional hearings.

They are up against a former Marine and FBI director who has already said that he wants the report to speak for itself and has demonstrated in prior hearings that he is unlikely to be chatty or to buckle under partisan pressure.

Schiff expects Mueller to repeat the report’s careful phrasing and “undoubtedly have lots of reasons to refuse to answer questions,” such as declining to interfere with an ongoing investigation or to speculate beyond the report.

Mueller is perhaps the most sought-after witness in this session of Congress. About two-thirds of the public, according to a recent CNN poll — and members of Congress of both parties — want to hear from him.

“People won’t believe me if I tell them, ‘I read the Mueller report. This is what it says,’ ” said Rep. Lou Correa (D-Santa Ana), a member of the Judiciary Committee.

“But if Mueller can tell us, ‘I’m Mueller. This is my report. This is what I found out,’ then maybe people will begin to believe it.”