President Donald Trump has been branded a “disgraced demagogue” by former CIA director John Brennan following the sacking of FBI deputy director Andrew McCabe, as Mr Trump’s feud with the bureau shows few signs of abating.

Mr McCabe said after his dismissal, which came just two days before he was due to retire and claim a number of government pension benefits, that it was the result of him being a crucial witness regarding whether Mr Trump obstructed a federal investigation into possible collusion with Russia by members of his campaign team.

Mr Trump had welcomed the dismissal of Mr McCabe – who he has frequently taunted both publicly and in private – as “a great day for democracy,” which led to the rebuke by Mr Brennan.

Attorney General Jeff Sessions said late on Friday that he felt justified in firing Mr McCabe after the Justice Department’s internal watchdog said in a report – the contents of which have not yet been made public – that he leaked information to reporters and misled investigators about his actions.

Mr Sessions said Mr McCabe had “made an unauthorised disclosure to the news media and lacked candour – including under oath – on multiple occasions”.

“The FBI expects every employee to adhere to the highest standards of honesty, integrity and accountability,” Mr Sessions added.

Mr McCabe has denied these allegations and called his firing part of a concerted effort by the Trump administration to discredit the FBI. “This attack on my credibility is one part of a larger effort not just to slander me personally, but to taint the FBI, law enforcement, and intelligence professionals more generally,” McCabe said. “It is part of this Administration’s ongoing war on the FBI and the efforts of the Special Counsel investigation.”

The biggest names involved in the Trump-Russia investigation Show all 17 1 /17 The biggest names involved in the Trump-Russia investigation The biggest names involved in the Trump-Russia investigation Paul Manafort Mr Manafort is a Republican strategist and former Trump campaign manager. He resigned from that post over questions about his extensive lobbying overseas, including in Ukraine where he represented pro-Russian interests. Mr Manafort turned himself in at FBI headquarters to special counsel Robert Mueller’s team on Oct 30, 2017, after he was indicted under seal on charges that include conspiracy against the United States, conspiracy to launder money, unregistered agent of a foreign principal, false and misleading US Foreign Agents Registration Act statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts. Getty The biggest names involved in the Trump-Russia investigation Rick Gates Mr Gates joined the Trump team in spring 2016, and served as a top aide until he left to work at the Republican National Committee after the departure of former Trump campaign manager Paul Manafort. Mr Gates' had previously worked on several presidential campaigns, on international political campaigns in Europe and Africa, and had 15 years of political or financial experience with multinational firms, according to his bio. Mr Gates was indicted alongside Mr Manafort by special counsel Robert Mueller's team on charges that include conspiracy against the United States, conspiracy to launder money, unregistered agent of a foreign principal, false and misleading US Foreign Agents Registration Act statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts. AP The biggest names involved in the Trump-Russia investigation George Papadopoulos George Papadopoulos was a former foreign policy adviser for the Trump campaign, having joined around March 2016. Mr Papadopoulos plead guilty to federal charges for lying to the FBI as a part of a cooperation agreement with Special Counsel Robert Mueller's investigation. Mr Papadopoulos claimed in an interview with the FBI that he had made contacts with Russian sources before joining the Trump campaign, but he actually began working with them after joining the team. Mr Papadopoulos allegedly took a meeting with a professor in London who reportedly told him that Russians had "dirt" on Hillary Clinton. The professor also allegedly introduced Mr Papadopoulos to a Russian who was said to have close ties to officials at the Russian Ministry of Foreign Affairs. Mr Papadopoulos also allegedly was in contact with a woman whom he incorrectly described in one email to others in the campaign as the "niece" to Russian President Vladimir Putin. Twitter The biggest names involved in the Trump-Russia investigation Donald Trump Jr The President's eldest son met with a Russian lawyer - Natalia Veselnitskaya - on 9 June 2016 at Trump Tower in New York. He said in an initial statement that the meeting was about Russia halting adoptions of its children by US citizens. Then, he said it was regarding the Magnitsky Act, a US law blacklisting Russian human rights abusers. In a final statement, Mr Trump Jr released a chain of emails that revealed he took the meeting in hopes of getting information Ms Veselnitskaya had about Hillary Clinton's alleged financial ties to Russia. He and the President called it standard "opposition research" in the course of campaigning and that no information came from the meeting. The meeting was set up by an intermediary, Rob Goldstone. Jared Kushner and Paul Manafort were also at the same meeting. Getty Images The biggest names involved in the Trump-Russia investigation Jared Kushner Mr Kushner is President Donald Trump's son-in-law and a key adviser to the White House. He met with a Russian banker appointed by Russian President Vladimir Putin in December. Mr Kushner has said he did so in his role as an adviser to Mr Trump while the bank says he did so as a private developer. Mr Kushner has also volunteered to testify in the Senate about his role helping to arrange meetings between Trump advisers and Russian Ambassador to the US Sergey Kislyak. Getty Images The biggest names involved in the Trump-Russia investigation Rob Goldstone Former tabloid journalist and now music publicist Rob Goldstone is a contact of the Trump family through the previously Trump-owned 2013 Miss Universe pageant, which took place in Moscow. In June 2016, he wrote to Donald Trump Jr offering a meeting with a Russian lawyer, Natalya Veselnitskaya, who had information about Hillary Clinton. Mr Goldstone was the intermediary for Russian pop star Emin Agalaraov and his father, real estate magnate Aras, who played a role in putting on the 2013 pageant. In an email chain released by Mr Trump Jr, Mr Goldstone seemed to indicate Russian government's support of Donald Trump's campaign. AP images The biggest names involved in the Trump-Russia investigation Aras and Emin Agalarov Aras Agalarov (R) is a wealthy Moscow-based real estate magnate and son Emin (L) is a pop star. Both played a role in putting on the previously Trump-owned 2013 Miss Universe pageant in Moscow. They allegedly had information about Hillary Clinton and offered that information to the Trump campaign through a lawyer with whom they had worked with, Natalia Veselnitskaya, and music publicist Rob Goldstone. Getty Images The biggest names involved in the Trump-Russia investigation Natalia Veselnitskaya Natalia Veselnitskaya is a Russian lawyer with ties to the Kremlin. She has worked on real estate issues and reportedly counted the FSB as a client in the past. She has ties to a Trump family connection, real estate magnate Aras Agalarov, who had helped set up the Trump-owned 2013 Miss Universe pageant which took place in Moscow. Ms Veselnitskaya met with Donald Trump Jr, Jared Kushner, and Paul Manafort in Trump Tower on 9 June 2016 but denies the allegation that she went there promising information on Hillary Clinton's alleged financial ties to Russia. She contends that the meeting was about the US adoptions of Russian children being stopped by Moscow as a reaction to the Magnitsky Act, a US law blacklisting Russian human rights abusers. Getty Images The biggest names involved in the Trump-Russia investigation Mike Flynn Mr Flynn was named as Trump's national security adviser but was forced to resign from his post for inappropriate communication with Russian Ambassador to the US Sergey Kislyak. He had misrepresented a conversation he had with Mr Kislyak to Vice President Mike Pence, telling him wrongly that he had not discussed sanctions with the Russian. Getty Images The biggest names involved in the Trump-Russia investigation Sergey Kislyak Mr Kislyak, the former longtime Russian ambassador to the US, is at the centre of the web said to connect President Donald Trump's campaign with Russia. Reuters The biggest names involved in the Trump-Russia investigation Roger Stone Mr Stone is a former Trump adviser who worked on the political campaigns of Richard Nixon, George HW Bush, and Ronald Reagan. 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Mr Page met with Russian Ambassador to the US Sergey Kislyak during the 2016 Republican National Convention in Cleveland. Mr Page had invested in oil companies connected to Russia and had admitted that US Russia sanctions had hurt his bottom line. Reuters The biggest names involved in the Trump-Russia investigation Jeffrey "JD" Gorden Mr Gordon met with Russian Ambassador to the US Sergey Kislyak during the 2016 Republian National Convention to discuss how the US and Russia could work together to combat Islamist extremism should then-Republican presidential candidate Donald Trump win the election. The meeting came days before a massive leak of DNC emails that has been connected to Russia. Creative Commons The biggest names involved in the Trump-Russia investigation James Comey Mr Comey was fired from his post as head of the FBI by President Donald Trump. The timing of Mr Comey's firing raised questions around whether or not the FBI's investigation into the Trump campaign may have played a role in the decision. Getty Images The biggest names involved in the Trump-Russia investigation Preet Bharara Mr Bahara refused, alongside 46 other US district attorney's across the country, to resign once President Donald Trump took office after previous assurances from Mr Trump that he would keep his job. Mr Bahara had been heading up several investigations including one into one of President Donald Trump's favorite cable television channels Fox News. Several investigations would lead back to that district, too, including those into Mr Trump's campaign ties to Russia, and Mr Trump's assertion that Trump Tower was wiretapped on orders from his predecessor. Getty Images The biggest names involved in the Trump-Russia investigation Sally Yates Ms Yates, a former Deputy Attorney General, was running the Justice Department while President Donald Trump's pick for attorney general awaited confirmation. Ms Yates was later fired by Mr Trump from her temporary post over her refusal to implement Mr Trump's first travel ban. She had also warned the White House about potential ties former National Security Adviser Michael Flynn to Russia after discovering those ties during the FBI's investigation into the Trump campaign's connections to Russia. Getty Images

The investigation that Mr McCabe referred to is the federal probe being run by Special Counsel Robert Mueller into Russia’s meddling in the 2016 presidential election and possible collusion between Russia and members of Mr Trump’s campaign team. Mr Trump and the White House have denied there was any collusion. The investigation into election meddling was originally led by former FBI Director James Comey before he himself was fired by Mr Trump in May last year.

Mr Comey later testified to a congressional panel that he had had conversations with Mr Trump where the president had asked him to think about dropping an investigation into the conduct of Mr Trump’s then-National Security Adviser Michael Flynn. The White House have denied such conversations taking place, although it is believed that Mr Mueller and his team are looking into whether Mr Comey’s firing could amount to obstruction of justice. Mr Flynn has since pleaded guilty to one count lying to the FBI, having been indicted by Mr Mueller.

In his statement, Mr McCabe alleged that the report used as the basis for his firing was sped up “only after” his testimony suggested that he would corroborate Mr Comey’s accounts of his conversations with Mr Trump. A source told the Associated Press that Mr McCabe had kept personal memos regarding interactions with the president. They are said to be similar to the ones maintained by Mr Comey.

In his tweet, Mr Trump also used the opportunity to attack Mr Comey as “sanctimonious” and called Mr McCabe’s firing “a great day for the hard working men and women of the FBI.” He asserted without elaboration that `Mr McCabe “knew all about the lies and corruption going on at the highest levels of the FBI.”

Responding to that, Mr Brennan, who led the CIA under President Barack Obama between 2013 and 2017, made his feelings clear about the reasons for Mr McCabe’s firing by tweeting about Mr Trump: “When the full extent of your venality, moral turpitude, and political corruption becomes known, you will take your rightful place as a disgraced demagogue in the dustbin of history.”

“You may scapegoat Andy McCabe, but you will not destroy America... America will triumph over you,” Mr Brennan’s tweet continued.

The former CIA director has previously described the President as “unstable, inept, inexperienced and unethical”.

Mr McCabe briefly served as director of the FBI between the firing of Mr Comey and the swearing-in of current director Christopher Wray. He played a crucial role in the bureau’s investigation into of Hillary Clinton’s use of a personal email server while she was Secretary of State, as well as the Clinton Foundation. That is in addition to playing a key role in the probe into Russia’s interference in the election.

Mr McCabe had been on leave from the FBI since January, when he abruptly left the deputy director position, with his subsequent dismissal putting his ability to collect his pension following 20 years of service at the bureau at risk. His removal will likely add to the turmoil surrounding the bureau’s relationship with the Trump administration.

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Mr McCabe came under scrutiny over an October 2016 news report about clashes between the FBI and the Department of Justice about about how aggressively the Clinton Foundation should be investigated. The watchdog office concluded that McCabe authorised FBI officials to speak to a Wall Street Journal reporter for that story and had kept back information about it.

In his statement, Mr McCabe said he had the authority to share information with journalists through the public affairs office and that he had honestly answered questions about whom he had spoken to and when, and that when he thought his answers were misunderstood, he contacted investigators to correct them.

At the time, Mr McCabe faced questions of partisanship, and both then and since he has been repeatedly been criticised by Mr Trump for being biased in favour of Hillary Clinton and because his wife Jill ran as a Democratic candidate for the Virginia State Senate. Ms McCabe had received campaign contributions from the political action committee of then-Virginia Governor Terry McAuliffe, a longtime Clinton friend, during her unsuccessful run. The FBI has said Mr McCabe received the necessary ethics approval about his wife’s candidacy and was not supervising the Clinton investigation at the time.

Mr McCabe suggested in his statement that he was trying to “set the record straight” about the FBI’s independence against the background of those allegations.

Mr Sessions faced a difficult decision over the firing. He risked inflaming the White House if he decided against dismissing Mr McCabe, but the timing of his forced departure is likely to upset rank-and-file members of the FBI.

The firing comes amid a number of resignations or firings of Trump administration staff in the past few weeks, including Secretary of State Rex Tillerson, Mr Trump’s economic adviser Gary Cohn and White House communications director Hope Hicks.