Donald Trump’s former campaign manager Paul Manafort has agreed to cooperate with federal prosecutors as part of a plea deal – creating a huge legal and political headache for the president.

As part of a deal in which the 69-year-old pleaded guilty to two charges, one of conspiracy against the United States and one of witness tampering, the man who was manager of the Trump campaign during the crucial period when he secured the Republican nomination for president, has agreed to help the team of special counsel Robert Mueller. A court in Washington DC said a 17-page document outlined the details of that agreement.

According to reports from inside the federal court in Washington, Manafort told judge Amy Berman Jackson: “I plead guilty.” The judge said Mr Manafort had agreed to be reinterviewed by Mr Mueller’s team, to hand over any documents and to testify before other investigative bodies – such as a congressional committee. He has agreed to do so without the presence of his lawyer. Yet NPR reported the cooperation agreement did not include matters involving the Trump campaign.

Either way, the White House very quickly moved to downplay the link between Mr Trump and anything that Manafort had admitted.

“This had absolutely nothing to do with the president or his victorious 2016 Presidential campaign. It is totally unrelated,” said Sarah Huckabee Sanders, White House press secretary.

Mr Trump’s main lawyer, Rudy Giuliani echoed her comments, saying that the plea has “nothing to do with President Trump or the Trump campaign” and said that “the president did nothing wrong”.

The plea hearing before US District Court judge Jackson means Manafort avoids going through a a second trial, which was scheduled to begin this month on charges of money laundering and lobbying violations. He was already facing eight to 10 years in prison after being convicted last month in Virginia on eight counts of bank and tax fraud and failing to disclose foreign bank accounts relating to $16m (£12m) laundered through shell companies overseas.

Friday’s drama was the latest victory for Mr Mueller, was who is investigating Russia’s interference in the 2016 election, and possible collusion by the Trump campaign. Mr Mueller, a former director of the FBI is also looking into whether Mr Trump obstructed justice. The president has repeatedly denied there was any such collusion and dismissed the probe as a “witch hunt”.

Donald Trump calls Paul Manafort 'a good man' following eight counts of bank and tax fraud

Manafort’s plea deal is by far the most consequential result yet from Mr Mueller’s 15-month probe into the circumstances surrounding Russia’s alleged interference with the election. Former national security adviser Michael Flynn, Manafort’s deputy Richard Gates and foreign policy advisor George Papadopoulos, have already pleaded to various charges, including lying to FBI investigators. None of charges are directly related to any misconduct by the president’s campaign.

Alex van der Zwaan, an attorney, pleaded guilty to lying to FBI investigators during the investigation, and was sentenced to 30 days in prison in April 2018. He was the first to be sentenced in the probe. Earlier this month, Papadopoulos was sentenced to 14 days for lying to agents.

Mr Trump has frequently pointed out that Manafort was only with his campaign for a few months; he joined in March 2016, with a focus on ensuring the former reality television star obtained sufficient commitments from delegates attending the Republican National Convention in Cleveland, Ohio, to secure the nomination. A month before the July convention, Manafort officially became manager of the campaign after Mr Trump fired Corey Lewandowski.

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In August, as controversy grew about Manafort’s work for former Ukrainian president Viktor Yanukovych, he was fired from the campaign and replaced by Steve Bannon and Kellyanne Conway.

One of the episodes that Manafort was present at, and which prosecutors have probably already questioned him about, was the June 2016 meeting at Trump Tower with Kremlin-linked lawyer Natalia Veselnitskaya. Also present at the meeting were Mr Trump’s eldest son, Donald Trump Jr, his son-in-law Jared Kusher, and Rob Goldstone, a British music producer who represented a Moscow-based singer and his powerful father, who already knew the Trump family.

The meeting had been organised after Mr Trump Jr was told the Russian lawyer had information about Hillary Clinton. In the end, he claimed she only wanted to talk about lifting US sanctions against Russia.

Mr Trump, who personally helped draft his son’s press statement about the incident, has dismissed the significance of the meeting on several occasions.

Speaking in Paris, where he was attending 2017 Bastille Day celebrations with Emanuel Macron, he told reporters: “My son is a wonderful young man. He took a meeting with a Russian lawyer, not a government lawyer, but a Russian lawyer. It was a short meeting. It was a meeting that went very, very quickly, very fast.”

He added: “I think from a practical standpoint most people would have taken that meeting. Politics isn’t the nicest business in the world, but it’s very standard.”

As part of the deal announced on Friday, Manafort, in addition to any jail time he may serve, has undertaken to forfeit four homes – three in New York, and one in Virginia. He will also give up the funds from five bank accounts.

The New York Times said on Friday that the filing document placed with the court detailed a rich trove of new information about the way Manafort sought to try to advance the interests of the former president of Ukraine, Viktor Yanukovych, between 2006 and 2014.

They refer to previously undisclosed work with “a senior Israeli government official” and two European consultants to discredit Yulia Tymoshenko, a political opponent who Mr Yanukovych’s government prosecuted and ultimately jailed.

It said Manafort admitted to coordinating with the Israeli official, who prosecutors did not identify, on an effort to pressure Jewish officials in the Obama administration, who Mr Manafort called “[O]bama jews” at the time.

“The Jewish community will take this out on Obama on election day if he does nothing,” Manafort wrote.

Democratic congressman Adam Schiff, the senior Democrat on the House Intelligence Committee, said Friday’s developments marked “another victory for Mueller”.

“If the resident moves to pardon Manafort or impede his cooperation in any way, it would constitute an attempt to obstruct justice,” he said.