Democrat Jamie Raskin begins by pointing out that the crime of "witness tampering" is punishable by up to 20 years in prison.

He points to a passage in Mueller's report which states that Trump tried "to encourage witnesses not to co-operate with the investigation".

Michael Cohen, Trump's ex-personal lawyer who arranged hush payments to women who allegedly had sex with Trump, he says, was intimidated by Trump after he turned on him and began testifying to federal officials.

He points to Trump's claim that Cohen's father-in-law had broken the law, saying it was an effort to pressure him to remain loyal to Trump.

Bob Mueller's words are getting different readings across the homepages of US media.

New York Times: "Trump Was 'Not Exculpated' by Report, Mueller Says, external"

Washington Post: "Democrats grill Mueller on obstruction, Republicans question probe's origins, external"

Fox News: "Flustered Mueller asks for questions to be repeated, blanks on Fusion GPS in contentious hearing, external"

Associated Press: "Mueller: I did not clear Trump of obstruction of justice, external"

Wall Street Journal: "Mueller Says His Report Didn't Exonerate Trump, external"

Democrats accuse Attorney General William Barr of framing the narrative around the Mueller probe - giving Trump a head start in his defence.

Barr's four page summary gave Trump his favourite talking point - "no obstruction, no collusion" - before Democrats and the public had a chance to see the report for themselves.

Here's how the release unfolded:

22 March: Mueller submits a confidential report on his findings to Attorney General William Barr

24 March: Barr issues a summary of what he called Mueller's "principal conclusions" and says there is insufficient evidence to charge Trump with a crime

18 April: Barr hold a news conference to say "no collusion, no obstruction". Trump triumphantly declares the report a "total exoneration"

29 May: Almost one month later, Mueller holds a news conference on his report where he disputes Trump's exoneration, saying instead there was insufficient evidence to charge the president with a crime

24 July: Testifying before Congress, Mueller says the president "was not exculpated" by the probe

There's a lot of name-dropping going on this morning.

Here's our guide on who's who in the drama to end all dramas.

Democrat Eric Swalwell, who recently dropped out of the 2020 Democratic race, asked if Mueller agreed with a letter from 1,000 former federal prosecutors who have said Trump could have been charged if he was not president.

"They have a different case," Mueller responds, in reference to other people who have been charged with obstruction.

Former New York Mayor Rudy Giuliani, a lawyer and unofficial aide to Trump, has taken to Twitter to call Mueller "pathetic" and a "lap dog" for Democrats.

"An unsuccessful attempt to obstruct justice is still a crime, right?" asks Democrat David Cicilline.

"Right," responds Mueller.

Trump has frequently said it would be impossible for him to obstruct justice, because there was no underlying crime to obstruct.

Mueller says that an attempt to interfere in any investigation could be regarded as obstruction.

Sarah Huckabee Sanders - who stepped down from her post as White House press secretary last month - calls Mueller's testimony a vindication of her former boss.

Republican Ken Buck criticises Mueller for declining to charge the president but then holding a news conference about his decision.

He also says Mueller "unfairly" made Trump have to prove his own innocence.

Buck then asks if the president could be charged with a crime after he leaves office.

Mueller confirms again: "Yes."

New York Democrat Hakeem Jeffries says that "terminating the head of an investigation constitutes a criminal act", in a reference to Trump's attempts to have Mueller removed.

Mueller says it is correct that Trump stated: "Mueller has to go".

Jeffries says Trump committed an "obstructive act, connected to a criminal proceeding, and did so with criminal intent".

"I don't subscribe necessarily to the way you analysed that," Mueller responds.

"One way or another, Trump has to go," says Jeffries, who has been discussed as a possible future Speaker of the House.

Republicans have focused their questioning on the Steele dossier.

In January 2017, a secret dossier was leaked to the press. It had been compiled by a former British intelligence official and Russia expert, Christopher Steele, who had been paid to investigate Mr Trump's ties to Russia.

The dossier alleged Moscow had compromising material on Mr Trump, including claims he was once recorded with prostitutes at a Moscow hotel during a 2013 trip for one of his Miss Universe pageants. Mr Trump emphatically denies this.

The file purported to show financial and personal links between Mr Trump, his advisers and Moscow. It also suggested the Kremlin had cultivated Mr Trump for years before he ran for president.

More on the Steele dossier:

• Trump-Russia affair: Key questions answered
• Defamation case against Christopher Steele dismissed
• Trump's 'Russia' dossier

US twitter is alight with tweets about today's testimony.

Here are some of the names trending this morning.

Mueller: 1.28m tweets

Jim Jordan: 87.7k tweets

Louie Gohmert: 21.8k tweets

Doug Collins: 45.4k tweets

John Ratcliffe: 38.2k tweets

Jerry Nadler: 92.3k tweets

Republican Matt Gaetz also gets into the Steele dossier, which Mueller says wasn't in his purview.

Gaetz all but shouts at the former special counsel about how it should be in his purview as it's related to Russian interference.

He says Mueller was "loquacious" about other topics regarding the president and his campaign.

"What's missing here is that this is under investigation elsewhere in the Department of Justice," Mueller responds. "And consequently it's not within my purview."

"When people associated with Trump lied, you threw the book at them," Gaetz goes on to say.

The president has tweeted for the first time since the hearing began.

The New York Times' Maggie Haberman points out how members of Trump's team have tried to shape this hearing as a "do-over".

She says that's a fair criticism, given how today's hearing is mostly going over information that was already publicly revealed in the Mueller report.

NYT Congressional correspondent Nicholas Fandos says he agrees with her analysis, adding that Democrats on the committee "are investigating possible obstruction of justice and abuse of power by Trump, but doing so, they are mostly riding Mueller’s coat-tails".

Image source, Reuters

Donald McGahn served as White House counsel for nearly two years before his resignation in October 2018 to join a law firm that represents the Trump campaign.

He was interviewed for 30 hours by the Mueller team and was frequently cited in the 448-page report.

The Mueller report detailed how Mr McGahn felt the president had pressured him to fire Mueller and, later, write a memo saying that Trump had issued no such directive.

In May, McGahn refused a subpoena to testify before the House Judiciary Committee, where Mueller appears today, after the White House directed him to shirk their invitation.

His name has popped up several times today, as Democrats believe Trump's effort to convince him to fire Mueller paints the clearest picture of obstruction of justice for the average American voter.

Jim Jordan, a vocal Trump supporter, gets into how the investigation began: George Papadopoulos.

"How'd he find out?" Jordan asks. Mueller says he can't get into it.

"Yes you can, because you wrote about it!" Jordan responds. "Joseph Mifsud."

(He's the Maltese professor who told Papadopoulos that Russians had "dirt" on Hillary Clinton.)

Jordan asks about charging decisions and whether Mueller interviewed Mifsud - Mueller says he can't get into it.

Image source, Getty Images

"You can charge all kinds of people who are around the president with false statements but the guy who launches everything, the guy who puts the whole story in motion, you can't charge him."

Mueller responds that he doesn't fully agree with those characterisations.

"The president was falsely accused of conspiracy," Jordan says. "You do a 22-month investigation, you find no conspiracy, and what's the Democrats want to do? They want to keep investigating."

He says it's maybe a better idea to figure out how all the false accusations started - and that's what Attorney General Bill Barr (a Trump pick) is doing.

"They're gonna find out why we went through this three-year saga," he all-but shouts, hitting the desk.