Special counsel Robert Mueller has spoken publicly for the first time following the release of his report on Russian meddling in the 2016 election, saying that his investigation could not have charged Donald Trump with obstruction because of Department of Justice policy that prohibits charging a sitting president with a crime.

In a statement, Mr Mueller hinted that congress holds the authority to impeach a sitting president, and appeared to directly contradict attorney general William Barr’s interpretation of his report by saying that his office “would have said so” if his investigators “had confidence the president clearly did not commit a crime”.

He continued, noting that congress has the authority to impeach a president, not the Department of Justice, which is a part of the executive branch of the US government.

“The constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing,” Mr Mueller said, noting that his team had followed protocol in not charging the president – even under seal – because it would be unfair to charge an individual whose case could not actually be adjudicated. “It would be unfair to potentially accuse somebody of a crime when there can be no court resolution to the actual charge.”

Mueller investigation: The key figures Show all 12 1 /12 Mueller investigation: The key figures Mueller investigation: The key figures Robert Mueller is the special counsel overseeing the investigation into Russia's meddling in the 2016 election, and potential obstruction of justice by the president. Mr Mueller has a pristine reputation in Washington, where he was previously in charge of the FBI. Throughout his investigation, he and his team have been notoriously tight lipped about what they know and where their investigation has led. REUTERS Mueller investigation: The key figures Former FBI director James Comey was the catalyst that led to the appointment of special counsel Robert Mueller. Mr Comey was fired by the president after Mr Trump reportedly asked him to drop his own Russia investigation. Mr Trump has long maintained that the investigation is a "witch hunt". AFP/Getty Images Mueller investigation: The key figures Deputy attorney general Rod Rosenstein had authority over the special counsel investigation for much of the two years it has been active. Mr Rosenstein found himself with that responsibility after then-attorney general Jeff Sessions recused himself from that oversight. AP Mueller investigation: The key figures Attorney general Jeff Sessions's decision to recuse himself from oversight of the special counsel investigation may have cost him his job in the end. Mr Sessions resigned last year, after weathering a contentious relationship with Donald Trump who vocally criticised his attorney general for taking a step back. Mr Sessions recused himself from the oversight citing longstanding Justice Department rules to not be involved in investigations overseeing campaigns that officials were apart of. AP Mueller investigation: The key figures Attorney General William Barr is currently responsible for oversight of the special counsel investigation. Mr Barr's office will be the first to receive the Mueller report when it is finished. His office will then determine what portion or version of that report should be delivered to Congress, and also made public. EPA Mueller investigation: The key figures Michal Cohn is the president's former personal lawyer, who has been helping the special counsel investigation as a part of a plea deal over financial crimes, and campaign finance crimes, he has pleaded guilty to. Among those crimes, Cohen admitted to facilitating $130,000 in hush money payments to adult film actress Stormy Daniels during the 2016 campaign. Cohen has said he did so at the direction of Mr Trump. Cohen has also admitted that he maintained contacts with Russian officials about a potential Trump real estate project in Moscow for months longer than Mr Trump and others admitted. The talks continued well into 2016 during the campaign, he has said. AP Mueller investigation: The key figures Stormy Daniels has alleged that she had an affair with Donald Trump in 2006, soon after Melania Trump gave birth to Baron Trump. The accusation is of particular importance as a result of the $130,000 hush money payment she received to keep quiet about the affair during the 2016 campaign. AP Mueller investigation: The key figures Paul Manafort was Donald Trump's former campaign chairman. Manafort was charged alongside Rick Gates for a slew of financial crimes, and was convicted on several counts in a Virginia court. He then pleaded guilty to separate charges filed in a Washington court. Manafort has been sentenced to just 7.5 years in prison for his crimes — in spite of recommendations from the special counsel's office for a much harsher sentence. AP Mueller investigation: The key figures George Papadopoulos was one of the first individuals associated with the Trump campaign to be charged by the Mueller probe. He ultimately received a 14 day prison sentence for lying to investigators about contacts he had with Russian officials. AP Mueller investigation: The key figures Roger Stone is a well known political fixer and operative, who has made a name for himself for some dirty tactics. He has been charged by the Mueller probe earlier this year, and he has been said to have had prior knowledge that WikiLeaks planned on publishing stolen emails from the Hillary Clinton campaign in 2016. Getty Images Mueller investigation: The key figures Rick Gates was charged alongside former Trump campaign chairman Paul Manafort for a range of crimes. Gates, who worked alongside Manafort for a pro-Russia Ukrainian political party. The two were charged with conspiracy and financial crimes. Gates pleaded guilty. AP Mueller investigation: The key figures Former national security adviser Michael Flynn was one of the first casualties of the Russia scandal, and was forced out of his position in the White House weeks after Donald Trump took office. Flynn pleaded guilty in 2017 to "willfully" making fraudulent statements about contacts he had with Russian officials including former Russian ambassador to the US Sergey Kislyak. Flynn then lied to Vice President Mike Pence about that contact. REUTERS

Beyond obstruction, Mr Mueller defended his office’s investigation, and stated that the findings of Russian meddling in the election were of great importance to the American people.

“There were multiple, systemic efforts to interfere in our election,” Mr Mueller said. “And that allegation deserves the attention of every American.”

Soon after Mr Mueller’s statement, Mr Trump responded on Twitter claiming his innocence despite the retiring special counsel’s comments.

“Nothing changes from the Mueller report. There was insufficient evidence and therefore, in our country, a person is innocent,” Mr Trump said. “The case is closed! Thank you.”

Robert Mueller hints he was blocked from charging Trump in damning resignation speech

Press secretary Sarah Sanders also weighed in, claiming that Mr Mueller’s report made it clear that there was “no collusion, no conspiracy”, and noted that the Department of Justice had determined not to charge the president with obstruction.

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“The special counsel has completed the investigation, closed his office, and has closed the case,” Ms Sanders said in a statement. “Mr Mueller explicitly said that he has nothing to add beyond the report, and therefore, does not plan to testify before congress. The report was clear – there was no collusion, no conspiracy – and the Department of Justice confirmed there was no obstruction. Special counsel Mueller also stated that attorney general Barr acted in good faith in his handling of the report. After two years, the special counsel is moving on with his life, and everyone else should do the same.”

The Democrats responded to Mr Mueller’s report by calling for further punitive action against the president, apparently sensing that Mr Mueller had not meant to exonerate the president.

That includes 2020 presidential candidates hoping to take Mr Trump on next year in the general election. Among those are Elizabeth Warren, Beto O’Rourke, and Julian Castro – all of whom had come out forcefully in favour of impeachment previously.

“Mueller leaves no doubt: 1) He didn’t exonerate the president because there is evidence he committed crimes. 2) Justice Department policy prevented him from charging the president with any crimes. 3) The constitution leaves it up to congress to act – and that’s impeachment,” Ms Warren tweeted.

Newcomers to that line of thinking include Cory Booker and Kamala Harris, who both said they believe Democrats in the house must now act.

“What Robert Mueller basically did was return an impeachment referral. Now it is up to congress to hold this president accountable,” Ms Harris tweeted. “We need to start impeachment proceedings. It’s our constitutional obligation.”

Mr Booker said the Trump administration “has continued to stonewall congress’s oversight” in a statement on Twitter that made his views explicit on the issue for the first time.

“Robert Mueller’s statement makes it clear: Congress has a legal and moral obligation ot begin impeachment proceedings immediately,” Mr Booker said.

Democrats in the house, meanwhile, were less explicit. Jerry Nadler, the chairman of the House Judiciary Committee, said in a statement that the president has been “lying about the special counsel’s findings”, and promised action in congress.

“Given that special counsel Mueller was unable to pursue criminal charges against the president, it falls to congress to respond to the crimes, lies and other wrongdoings of President Trump – and we will do so,” Mr Nadler said in a statement. “No one, not even the president of the United States, is above the law.”

House speaker Nancy Pelosi, who has resisted the measure previously by saying that the house must conclude its investigations, thanked Mr Mueller for his service as special counsel and challenged the policy that kept him from charging Mr Trump. But, she did not call for the president’s impeachment.

“Despite Department of Justice policy to the contrary, no one is above the law – not even the president,” Ms Pelosi said in a statement.