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Mr Gergen, who served as an adviser for four US Presidents including Richard Nixon and Bill Clinton, said it appears Mr Trump was intentionally attempting to influence the course of the FBI probe. Speaking on CNN, Mr Gergen said: “I was in the Nixon administration and I thought after watching the Clinton impeachment that I’d never see another one, but I think we’re in impeachment territory now.

GETTY/CNN Mr Gergen suggested Trump's presidency 'is starting to come apart'

“Obstruction of justice was the number one charge against Nixon that brought him down, obstruction of justice was the number one charge against Bill Clinton, which led to his indictment in the House that he won in the Senate.” He added: “I cannot tell you if it meets all the legal definitions but from a lay point of view, it looks like he was trying to impede the investigation. “He was using his power to do that and when James Comey didn’t go along with him… he fired him, which I think is also relevant to the question of what he was trying to do.

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I cannot tell you if it meets all the legal definitions but from a lay point of view, it looks like he was trying to impede the investigation David Gergen

“This is of enormous consequence for his presidency - if you look at the three bombshells we’ve had: the Comey firing last week, then the sharing of this highly classified information with the Russians of all people, and now telling Comey to drop the case - what we see is a presidency that’s starting to come apart.” On Tuesday, the New York Times reported that President Trump asked Mr Comey to end an investigation into alleged ties between former national security adviser Michael Flynn and Russia.

GETTY Mr Gergen (R) alongside President Clinton in 1993

The US President allegedly told Mr Comey, “I hope you can let this go”, according to two sources who spoke to the New York Times. An associate of Mr Comey, who has seen the memo, reportedly said that the details of the document were accurate.

GETTY FBI Director James Comey was sensationally sacked last week

The memo, which was reportedly written by the former FBI director himself, was created after a meeting between Mr Comey and the US President in February. The White House quickly responded to the news by issuing a statement, denying that the President had told Mr Comey to drop his investigation while acknowledging a “conversation” had happened between the pair. The statement said: “While the President has repeatedly expressed his view that General Flynn is a decent man who served and protected our country, the President has never asked Mr Comey or anyone else to end any investigation, including any investigation involving General Flynn.