Washington (CNN) Former special counsel Robert Mueller's testimony Wednesday has the potential to either kickstart an impeachment inquiry into President Donald Trump -- or put the nail in the coffin of the Democratic efforts to impeach the President.

Lawmakers on the House Judiciary and Intelligence Committees have been intensely preparing for their opportunity to question Mueller in back-to-back hearings, and Mueller's been practicing as well. Here's what to watch for when Mueller arrives on Capitol Hill Wednesday morning:

What kind of witness is Mueller?

The former special counsel has decades of experience testifying before Congress, but the last time he did it was more than six years ago during his final weeks serving as FBI director.

In his two years as special counsel, Mueller spoke publicly just once: in his last week . He took no questions from the reporters in attendance.

Mueller's public silence makes him a wild card for the lawmakers preparing to question him. They don't know how Mueller will react: Will he be combative? Collegial? Answer with short, one-word responses? Or try to filibuster and run out the clock?

In his public statement, Mueller said that he did not want to testify before Congress and be part of the political circus, although he ultimately agreed to appear under subpoena. But lawmakers and staff preparing questions will have to take their best guesses as to how Mueller's reluctance translates into his responses -- and how they can best elicit the answers they're looking for.

Mueller has been preparing for the hearing with a small group of aides at his former law firm, Wilmer Hale, and a spokesman said he "is someone who comes to the table fully prepared and he's going to be ready on Wednesday."

Will Mueller go beyond the report?

The biggest looming question that Democrats would like answered Wednesday: Would you have charged Trump if he were not a sitting President?

It's a question that Mueller is unlikely to answer -- he said in May his office relied on the Justice Department's guidelines that a sitting President cannot be indicted -- but Democrats are hopeful Mueller will engage with them on some of their questions that go beyond the 448 pages Mueller's team submitted in March.

The Justice Department wrote in a letter to Mueller on Monday that he should not do so. "Any testimony must remain within the boundaries of your public report because matters within the scope of your investigation were covered by executive privilege, including information protected by law enforcement, deliberative process, attorney work product and presidential communications privileges," the DOJ wrote in the letter it said was in response to Mueller's request for guidance.

That doesn't mean Democrats won't try.

For instance, Democrats are interested in Mueller's assessment of the numerous contacts between Trump's team and Russia -- even if there wasn't enough evidence to charge a criminal conspiracy.

And Republicans, too, want to press Mueller on issues outside the contents of the report , such as the FBI's foreign surveillance warrant obtained for a Trump adviser and the makeup of the special counsel's team.

Mueller's spokesman Jim Popkin said Monday that the former special counsel's testimony was expected to stay within his report, as Mueller indicated in his May public statement when he said: "The report is my testimony."

"If you listen to that statement, he made it clear that you can basically expect him to stick to the report," Popkin said.

Which obstruction episodes do Democrats focus on?

Judiciary Committee aides say Democrats on the panel plan to focus on five episodes of obstruction detailed in Mueller's report.

Those episodes include what Democrats believe are the strongest cases of criminal conduct that Mueller documented related to obstruction, including Trump's efforts to fire the special counsel, to have then-Attorney General Jeff Sessions un-recuse himself and to tamper with witnesses like his former campaign chairman Paul Manafort.

While Democrats didn't say they would ignore the other obstruction episodes in the Mueller report, the fact they plan to highlight five provides an insight into their thinking about which details in Mueller's obstruction investigation are most damning to the President. Should Democrats decide to pursue an impeachment inquiry, these are likely to be the same obstruction episodes they turn to.

Can Dems combat Trump's 'no collusion' mantra?

In Mueller's obstruction investigation, the special counsel made a point to publicly state that his team could not exonerate the President. But Mueller's report directly says that the investigation did not establish a criminal conspiracy between Trump's team and the Russian government.

Trump and his Republican allies have quickly seized on the conclusion to claim that Mueller found no collusion -- and to attack Democrats like House Intelligence Chairman Adam Schiff for claiming there was evidence of collusion.

But to Schiff and other Democrats on the House Intelligence Committee, no crime does not mean no collusion. In fact, Schiff has not backed down from his charge that the contacts between Trump's team and Russia did add up to collusion -- and it's a point that Schiff is likely to try to hammer home with the public during the second Mueller hearing.

Does Mueller's testimony paint a picture?

Democrats say they insisted on having Mueller testify, even after he expressed a desire not to, because the public needed to hear from the former special counsel directly. Democratic lawmakers and aides say the reality is the vast majority of the public didn't read the Mueller report -- and they argue the public's perception was tainted by Attorney General William Barr's misrepresentation of the special counsel's findings.

What Democrats are banking on is that even if Mueller only discusses the contents of his report, his televised testimony detailing the episodes in the report will sway public opinion on the special counsel's investigation.

Of course, there's no guarantee that Mueller will get into such details. He could simply tell lawmakers to read the report rather than elaborate on its contents, for instance. But Democrats are betting that the movie version of Mueller could be a blockbuster even if the book was not.

How does Trump react?

The President -- and his Twitter feed -- will be an interested observer. On Friday, Trump said he would not watch the Mueller hearing. Then Monday, the President said he might "see a little bit of it."

Trump tweeted Monday morning that Mueller "should not be given another bite at the apple" before attacking the special counsel and stating: "NO COLLUSION, NO OBSTRUCTION!"

Will Trump tweet on Wednesday before or after the report? Will he react to Mueller on Twitter in real time? Even if Trump isn't active on social media, he'll have a chance to respond to Mueller on his way to a fundraiser in West Virginia Wednesday evening.

How aggressive are Republicans with Mueller?

Some of the Republicans who have been the most vocal Mueller critics sit on the Judiciary and Intelligence Committees, and they're likely to press the former special counsel about everything from the anti-Trump text messages sent by members of his team to the Foreign Intelligence Surveillance Act (FISA) Warrant the FBI obtained on former Trump adviser Carter Page.

Republicans' goal will be to undercut the Democratic narrative that Mueller's report contained damaging information about the President, and they've got a key conclusion from Mueller to do it: he did not establish a criminal conspiracy with Russia.

But some Republicans will also look to knock down the legitimacy of the special counsel's investigation in the first place, and their exchanges with Mueller could sow doubts about his work -- or Mueller's responses could bolster the case that the probe he conducted was legitimate, not a "witch hunt."

As a veteran congressional witness, Mueller is likely to be as prepared for Democrats trying to get him to say Trump committed a crime as he is for Republicans trying to delegitimize his two-year investigation, and those exchanges could wind up among the most memorable.

Can Democrats stay on script?

Democrats and Republicans on both committees have been intensely preparing for the Mueller hearings, working on sharpening questions and holding mock hearings to be ready for Wednesday's big show.

But the stakes may be highest for Democrats, who only have a limited time with Mueller after issuing a subpoena to compel his testimony.

They want to make the most that time, and lawmakers say that will require all of them to stay on script and on message, asking Mueller questions and not delivering long, wind-up speeches -- a task that's not an easy one for a Congress that's used to speechifying.

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The effort is particularly important for Democrats on the Judiciary Committee, which negotiated an extra hour with Mueller but still has to fit 41 members into three hours -- which would require some members to give back a chunk of their valuable five minutes to question Mueller.

What does Mueller say about Barr?

Just as lawmakers hope to get Mueller to engage about his investigation beyond the report, Democrats are likely to press Mueller about his views on Barr's role in the investigation.

The attorney general allowed most of the Mueller report to be released, but Barr has been slammed by Democrats, accused of trying to deceive the public about Mueller's report by putting out a misleading summary that distorted Mueller's conclusions.

Mueller himself sent two letters to Barr , including one that objected to the way the report was being characterized and urging him to release the executive summaries that had been written for public dissemination.

Barr also decided to make a determination that the President did not commit obstruction of justice after Mueller did not come to a conclusion.

Mueller is sure to be asked about his correspondence with Barr and whether he agreed with the attorney general's decision that Trump did not commit obstruction, and Mueller's answer -- or non-answer -- could be a key point in the hearings.

Will Mueller's testimony create momentum for impeachment?

Among Democrats advocating for beginning an impeachment inquiry , Mueller's testimony is seen as a key benchmark for persuading the public -- and House Speaker Nancy Pelosi, who has resisted those calls thus far.

A document on the Mueller report that was being circulated to Democrats by Pelosi Tuesday said that her caucus was "now advancing legislation to aggressively address the crimes, corruption and cover-up exposed in the Mueller report" -- but it made no mention of impeachment.

So far, roughly 90 House Democrats out of the 235-member caucus have publicly said they support impeachment or an impeachment inquiry. There could be another wave of Democrats waiting until after Mueller's testimony to decide whether to join their colleagues -- who have the potential to create real momentum for an impeachment inquiry if they sign on to the effort en masse in the hours after the hearing.

At the same time, if Mueller's testimony is considered a bust for Democrats, it could mark the end of the impeachment push. His appearance comes just two days before the House is set to leave for a month-long congressional recess, giving the impeachment caucus little time to try to bolster their ranks before lawmakers scatter across their country back to their districts.