Former special counsel Robert Mueller's hearing will be a major test for pro-impeachment advocates looking to see whether his long-awaited testimony on the Russia investigation will move more House Democrats to support opening an impeachment inquiry against President Donald Trump.

Mueller will testify Wednesday in back-to-back House hearings about his nearly two-year investigation into Russian interference in the 2016 election that's expected to draw large crowds and nonstop news coverage. He'll start his day at 8:30 a.m. with a three-hour hearing before the Judiciary Committee. After that, he'll testify for two hours before the intelligence committee.

Some see Mueller's testimony as their biggest opportunity yet to get more Democrats behind impeachment as well as to sway public opinion among Americans who didn't actually read the contents of the special counsel's 448-page report. Impeachment continues to be a divisive issue for the caucus, and public polling shows little support for beginning proceedings.

Mueller's report details Russian meddling in 2016 through a social media disinformation campaign but said the Trump campaign didn't conspire with Russia. Mueller also looked into whether Trump obstructed justice by seeking to impede the special counsel's probe. Citing DOJ's guidelines, Mueller noted a sitting president can't be prosecuted but also wouldn't exonerate Trump.

With Mueller unlikely to go beyond those conclusions, much of the attention will likely pivot to the immediate reaction following Wednesday's hearings and how many more Democrats will be convinced to align with pro-impeachment lawmakers: Will it be a ripple or wave?

Mueller's first public comments about the investigation in May sparked an uptick in Democrats supporting an impeachment inquiry. And the pro-impeachment movement got another jolt after a vote on a resolution forced for consideration by Rep. Al Green, D-Texas. While the House overwhelmingly voted to kill that effort, it put several more House Democrats on the record about impeachment, with 95 Democrats opposing tabling it.

Green's impeachment push was ignited by Trump's critical tweets about four female lawmakers of color that the House recently condemned as "racist." The president tweeted that Reps. Alexandria Ocasio-Cortez of New York, Rashida Tlaib of Michigan, Ilhan Omar of Minnesota and Ayanna Pressley of Massachusetts should "go back and help fix the totally broken and crime infested places from which they came." All four members are U.S. citizens.

Over 90 Democrats – and now-independent Rep. Justin Amash of Michigan – support at least an impeachment inquiry, while some are still wary of immediately pursuing impeachment. More than half of the members on the Judiciary and Intelligence committees, who will be tasked with questioning Mueller, back an impeachment inquiry.

While the number has grown in recent months, that's still less than half of the 235 House Democratic caucus. All House Republicans are opposed to impeachment, and any resolution would hit a wall in the GOP-controlled Senate.

Cartoons on the Mueller Report View All 45 Images

There has been strong pushback from Democratic leadership, including House Speaker Nancy Pelosi. The California Democrat has repeatedly said to "follow the facts" and follow through with the dozens of investigations into Trump's administration that are underway. She's also tasked with protecting the House majority and the dozens of freshman Democrats who represent Trump districts.

House Judiciary Committee Chairman Jerry Nadler of New York told "Fox News Sunday" that Mueller's report shows "very substantial evidence" that Trump is "guilty of high crimes and misdemeanors" – the constitutional definition of an impeachable offense . But Nadler, who will be leading Wednesday's questioning during the first hearing, has not publicly said he supports an impeachment inquiry.

Mueller has indicated he won't go beyond what's in the report, saying in May that "the report is my testimony." The Justice Department wrote a letter to Mueller on Monday advising him to stick to the report and not discuss the evidence.

Still, Democrats are banking on the fact that many Americans have read little or none of the report and hope they'll get some answers about his decision-making.

Mueller will likely face questioning about his decision not to prosecute or exonerate Trump on obstruction of justice as well as why he didn't subpoena Trump to testify during the investigation. The president instead submitted written responses to Mueller's team.

He may also be pressed about his relationship with Attorney General William Barr, who's been a loyal Trump official, and if Mueller took any issue with his four-page memo of the lengthy report.

Republicans have been sharply critical of Mueller, whom they have painted as a partisan, and have accused Democrats of wasting time and money in dragging out a politically motivated probe. Republicans have said they want to get answers from Mueller on the origins of his investigation.

"There's going to be a lot of questions for what he did say, what he didn't say, and how this thing started," said Rep. Doug Collins of Georgia, ranking member on the Judiciary Committee, according to The Associated Press . "This is the time that the Democrats have got to show on their end how much time they have been wasting of our committee and how we have not been getting things done because they simply don't like this president, who was elected by the people in 2016, and they're just trying to derail him for 2020."

Trump has repeatedly called Mueller's inquiry a "witch hunt" and has claimed "complete and total exoneration." While speaking with reporters alongside Pakistani Prime Minister Imran Khan on Monday, Trump criticized last week's impeachment resolution vote, offering rare praise for Democrats who voted to table the measure.

"I didn't know they'd do it. I have a lot of respect for the Democrats who voted against it ... because they're doing the right thing for the country," Trump said.

Mueller's hearings come two days before Congress leaves town for a monthlong August recess. That timing could stymie potential impeachment momentum as members leave town. But it also gives a chance for members to take the temperature of their constituents to inform whether there's an appetite to pursue impeachment with over a year to go before the 2020 election.

