WASHINGTON - House Democrats are hoping Robert Mueller illuminates potential obstruction of justice by President Donald Trump and gives credence to their claim of an unlawful president for millions of Americans who will decide on Trump's political future.

Mueller's much-anticipated testimony Wednesday is a pivotal moment for congressional investigators, holding promise - and peril - for Democrats as they finally get their chance to question a reluctant witness about his nearly two-year investigation into Russian interference in the 2016 election and whether the president tried to derail the inquiry.

Democrats expect Mueller to describe in detail at least five of 10 episodes of possible obstruction that the former special counsel laid out in his report, which found insufficient evidence to show a conspiracy between the Trump campaign and Russia to influence the election and reached no conclusion about whether the president tried to block the probe.

Democrats, however, are divided on what they hope to get out of the long-awaited day of Mueller speaking to Congress and a nation. Ninety-two Democrats favor impeachment of Trump and consider Mueller's testimony their best shot at moving public sentiment toward ousting the president. Party leaders, reluctant to pursue an inquiry, are hoping the hearings inflict enough political damage to Trump to undermine his reelection bid in next year's election.

During a recent closed meeting, House Speaker Nancy Pelosi, D-Calif., argued that all Democrats need to do is let Mueller talk - particularly given that less than 3% of the country has read the 448-page redacted report, she said.

"I'd like to have a level of calmness - no drama - regarding the Mueller presentation," Pelosi told her colleagues, according to an individual in the room who spoke on the condition of anonymity to freely discuss internal talks. "The very fact that he is presenting is what we want, so many more people will be aware of the charges that are in the Mueller report."

Democrats do not expect major revelations from Mueller, who will testify for three hours before the House Judiciary Committee and two hours before the House Intelligence Committee. They expect his answers to be short and curt, and have crafted questions that they hope will elicit a narrative from Mueller of a president committing illegal acts who would have faced prosecution if not for Justice Department policy forbidding the indictment of a sitting president.

Mueller's team wrote in the report that it was bound by that policy from deciding or alleging - even privately - that Trump had committed a crime.

"We don't need anything dramatic from Robert Mueller," said Rep. Ted Lieu, D-Calif., a member of the House Judiciary Committee who favors impeachment. "We just need him to highlight the main parts of his report because it's such a damning report - and then we win."

Clearly feeling the pressure of the moment, Democrats have been practicing. Over the past few weeks, members of both committees have been holding one-on-one prep sessions, with aides playing Mueller and forcing lawmakers to respond to different scenarios, such as a reticent Mueller or a combative Mueller. Several lawmakers have had multiple sessions.

Privately, Pelosi has cautioned Democrats not to get carried away in their questioning, as overreach and grandstanding would undermine their goals for the hearings.

Democrats will be in the spotlight for their performance as much as Mueller. Academics, lawyers and former White House counsel John Dean, a key player in Watergate, have hardly created a ripple with their testimony. Congressional investigations have produced no blockbuster revelation seen as damaging to Trump, complicated in part by White House resistance to their inquiries.

At the same time, the party's liberal base has grown increasingly frustrated with what they see as ineffective oversight of the president.

"I think people recognize that this is a very important moment in our oversight responsibilities," said Rep. David Cicilline, D-R.I., when asked about the nervousness among Judiciary Committee members.

The two panels have taken the unusual step of coordinating their questioning. Judiciary Committee Democrats plan to focus on possible obstruction of justice, while members of the Intelligence Committee are intent on getting answers about Russia's contacts with the Trump campaign.

"We are operating under the expectation that most American citizens have not had a chance to read the paper report," said Rep. Adam Schiff, D-Calif., chairman of the Intelligence Committee. "And then we'll have questions for him that go beyond the report ... we don't recognize any limitations, there are none in law or statute or policy, and the attorney general has disregarded them anyway."

Over the nearly two-year investigation, the special counsel charged 34 people, including 26 Russian nationals, and secured guilty pleas from seven, including several high-level Trump campaign and administration officials. The investigation concluded in March, and the Justice Department in April released the office's report documenting its work.

Democrats argue that in his public statements, Attorney General William Barr mischaracterized the report as more favorable to Trump than it was meant to be, and have prepared to push back on the impressions he created.

Rep. Raja Krishnamoorthi, D-Ill., a member of the Intelligence Committee, wants to know "which relationships were so compromised that they still present security risks to the United States, even if they're not criminally prosecutable." Rep. Val Demings, D-Fla., who sits on both committees, wants to know why Mueller didn't push to interview Trump for his investigation and why he said he could not exonerate the president on obstruction.

On the Republican side, lawmakers see the hearings as an opportunity to bolster their case that the report cleared the president, while demanding a reckoning from Mueller for an investigation they argue was biased from the start.

"There's been a lot of concern about, you know, how this whole two-year trek got started and how things were done," said Rep. Douglas Collins, R-Ga., the ranking Republican on the Judiciary Committee. "At the end of the day, the report showed no collusion conclusively and no charge of obstruction. . . . We're just going to say: Why did we get put through this?"

Republicans also have been practicing. Some, including Trump ally Rep. Matt Gaetz, R-Fla., have studied videos of Mueller's congressional testimony from when he was FBI director, to better understand his moves. Judiciary Republicans recently held a closed mock hearing for their members.

"Robert Mueller is the LeBron James of using 300 words to say absolutely nothing," Gaetz said, a reference to the basketball star.

Republicans plan to highlight Mueller's finding that he could not establish a conspiracy between the Trump campaign and Russia; anti-Trump text messages discovered on the phones of two of Mueller's agents by an independent watchdog; and allegations that a salacious, unsubstantiated dossier authored by Trump's political adversaries triggered the probe.

The strategy holds potential promise with the GOP base, but also peril if lawmakers attack Mueller, a decorated Vietnam War veteran who has had a distinguished career serving both Republicans and Democrats. Yet that's exactly what Rep. Louie Gohmert, R-Texas, suggested he might do with his five minutes of questioning. The Trump ally has a self-published book titled "Mueller Unmasked," and he plans to raise those allegations.

House Intelligence Committee ranking member Rep. Devin Nunes, R-Calif., has also tried to discredit Mueller's testimony in advance, accusing Democrats of feeding Mueller "helpful phrases." In fact, no Democrat on the committee or aide has had direct contact with Mueller, according to a panel aide who spoke on the condition of anonymity to describe internal deliberations.

Privately, some Republicans acknowledge that they have to strike a balance, calling into question any adverse findings about the president but also ensuring that they don't appear too partisan in criticizing Mueller.

"The biggest risk that exists is that my colleagues on the Republican side of the aisle overreach and attack Bob Mueller, who was someone with a history of being a war hero, law enforcement professional, a patriotic American," said House Democratic Caucus Chairman Hakeem Jeffries of New York, a Judiciary panel member. "But the likelihood is, my Republican friends cannot help themselves, because they never miss an opportunity to bend over backward to please Donald Trump."