Mueller has left the hearing room as the first of his two hearings today ends.

All members may now submit additional questions over the next five days, Nadler says. And now the hearing is adjourned.

Democrat Veronica Escobar asks Mueller: "You explained that 'the opinion says that the Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrong doing'. That process...is that impeachment?"

Mueller again says he won't comment.

But Escobar says impeachment is one of the congressional processes listed in a footnote.

"From everything I have heard you say today, it's clear that anyone else would have been prosecuted based on the evidence available in your report. It now falls on us to hold President Trump accountable."

The BBC's Jon Sopel highlights a key moment from the hearing.

People on Twitter are posting pictures of their pets as a way of getting some light-hearted relief from the Mueller hearing.

Democrat Greg Stanton highlights Mueller's Republican background - being appointed by Ronald Reagan and George W Bush to law enforcement roles.

"In your entire career as a law enforcement official have you ever made a hiring decision based on a person's political affiliation?" Stanton asks.

"No," Mueller says.

He adds: "The capabilities we have shown in the report that's been discussed here today was the result of a team of agents and lawyers who were absolutely exemplary and hired because of the value they could contribute to getting the job done and get it done expeditiously."

Republican Mike Johnson ends questioning for the Republicans.

He says "millions of Americans maintain genuine concerns" about Mueller's report because of the "bias" of his investigating team, which "included no Republicans".

"You wouldn't answer any questions here today about the origins of this whole charade," he says after a long summary of Republican views on the hearing.

Mueller doesn't get a chance to speak for nearly all of it.

"Your report does not recommend impeachment, does it?" Johnson finally asks.

"I'm not going to talk about recommendations," Mueller says.

"That's one of the many things you wouldn't talk about today," comes the response.

US commentators are divided on how Robert Mueller is performing before Congress.

Some see him as a neutral referee, some see him as a pushover for the GOP, others celebrate the former FBI director for "finally" pushing back.

Joe Neguse, a Colorado Democrat, gets Mueller to confirm that Donald Trump Jr - the president's son - was the only participant at a Trump Tower meeting in 2016 that refused to be interviewed by Mueller.

That meeting was held after a Russian lawyer with links to the Kremlin offered damaging information about Hillary Clinton - Trump's 2016 political opponent.

Mueller confirms that Trump directed his aide Hope Hicks to claim that the meeting was held to discuss "Russian adoptions" although he knew that to be untrue.

Republican Kelly Armstrong of North Dakota asks about the composition of Mueller's team.

"Six of your lawyers donated $12,000 directly to Hillary Clinton," he says.

"We strove to hire those individuals who could do the job," Mueller responds. I'e been in this business for almost 25 years and in those 25 years, I have not had occasion once to ask somebody about their political affiliation. What I care about is the capability of the individual to do the job."

Mueller says: "We hired 19 lawyers - 14 of them were transferred from elsewhere in the Department of Justice."

"And half of them had a direct relationship political or personal with the opponent of the person you were investigating," Armstrong replies.

Armstrong ends by saying if the roles of Hillary Clinton and Donald Trump were switched in this inquiry, Democrats would be up in arms about conflict of interest.

Image source, Getty Images

Texas Democrat Sylvia Garcia asks about Roger Stone, who is accused of co-ordinating the release of stolen Democratic emails with Wikileaks.

"I feel uncomfortable discussing anything having to do with the Stone prosecution," he says, citing the ongoing investigation into Stone, an early Trump ally.

Stone is accused of lying to Congress about his contacts with Wikileaks. He is also charged with obstruction of justice and witness tampering.

Read more about Roger Stone here

Republican Greg Steube questions Mueller with a sharp tone.

"Did you obtain any evidence at all that any American voter changed their vote as a result of Russian election interference?"

Mueller says he can't speak to the imapct of interference as it was outside his purview, handled by other agencies.

Steube then asks when Mueller became aware of the fact that the Steele dossier was unverified. Mueller can't give a specific time.

Steube asks for more details about Christopher Steele. Mueller says it's being handled by others and he won't discuss more about the Steele dossier investigation - as he mentioned at the start of the hearing.

Steube asks: "You're not going to speak any more to it but you don't agree with my characterisation?"

Mueller agrees.

"I don't understand how if you interviewed an individual in the purview of this investigation how it's not within your purview to tell us about that interview," Steube snaps.

"You're unwilling to answer the questions of the American people."

Mueller confirms that he was interviewed by Trump in 2017 to discuss the FBI director job, but says the meeting was not to discuss himself applying for the job.

Trump has claimed multiple times, including today, that Mueller is bitter that he was denied the job.

New York Times commentators have been discussing the issue.

Image source, Twitter

Republican Ben Cline gets into legal theory.

People in the Justice Department disagreed with Mueller's application of legal theory regarding obstruction of justice, right? - he asks.

Mueller says he won't get into that.

Prosecutors have incorrectly applied the law before, correct?

Mueller agrees.

Cline follows the Republican trend of talking over some of Mueller's answers to continue questioning. Mueller appears to show some frustration.

Image source, Getty Images

Democrat Val Demmings, a former police chief, starts "lets talk about lies".

"Did other witnesses lie to you," she asks, besides those that were charged?

"I think there's probably a spectrum of witnesses in terms of those who are not telling the full truth and those that are outright liars," he responds.

She asks if "lies [by] Trump campaign officials and administration officials impeded your investigation".

"I would generally agree with that," says Mueller.

Despite his vows to ignore Mueller's testimony, US commentators - and Trump's own tweets - suggest that the president is keeping an eye on proceedings.

Image source, Twitter

Image source, Getty Images

Guy Reschenthaler attacks Mueller for publishing a report with "dirty laundry" details while not recommending charges.

"Did you allow people mentioned in the report to challenge how they were characterised?" the Republican lawmaker asks.

Mueller is not going to get into that.He later notes this case is also unique: "Most cases are not done in the context of the president."

"You did this knowing you were not going to recommend charges," Reschenthaler goes on to say. "The drafting and the publication of some of the material in this report without prosecution flies in the face of American justice."

Reschenthaler concludes: "I find this entire process un-American."

Washington Democratic Congresswoman Pramila Jayapal asks about Trump's statement that "flipping" witnesses should be outlawed.

She asks Mueller was "flipping means in this context".

"Having somebody co-operate in a criminal investigation," says the veteran prosecutor.

When Jayapal asks about the importance of witness co-operation in investigations, Mueller says he's "not going to characterise" that.

Jayapal says her point is that if anyone but Trump had attempted to convince former campaign chair Paul Manafort to not co-operate with investigators, they would have been charged with a crime.

Justice Department guidelines state that a sitting president cannot be charged with obstruction of justice.

Manafort has been sentenced to years in prison for bank and tax fraud after his crimes were discovered by the Mueller probe. The charges do not relate to his work for Trump.

Arizona Republican Debbie Lesko wants to know how many times Mueller cited the Washington Post in his report.

"I do not have knowledge of that figure," he responds.

"I counted about 60 times," Lesko says. She says she counted 75 times instances of the New York Times, and 25 mentions of Fox News.

"It looks like volume two is mostly regurgitated press stories," Lesko says.

"Honestly there's almost nothing in volume two that I couldn't already hear or know by having a $50 cable news subscription."

She runs out of time before Mueller answers a specific question about the use of news organisations and footnote explanations in his report.

California Republican Tom McClintock says "the problem" is that Mueller's report is not "an accurate reflection of the evidence".

He brings up Russian "troll farms" - groups of accounts spreading misleading content - and says Mueller's report linked these troll farms with the Russian government, leading to a judge excoriating him and Attorney General Bill Barr "for producing no evidence".

"You have left the clear impression throughout the country through your report that it was the Russian government behind the troll farms, yet when you're called upon to provide actual evidence in court you fail to do so."

Mueller says he disputes the characterisation.

After some more criticisms from McClintock, Mueller ends the discussion by stating his report has been thorough and fair.

The BBC's technology reporter Dave Lee explains the tactics of a Russian troll farm here.