The Democratic Party has filed a multimillion dollar lawsuit against the campaign of Donald Trump, the Russian government and Wikileaks, alleging all three conspired to swing the 2016 presidential election and saying the former reality television star did so “gleefully”.

In the latest twist to a saga that has consumed much of the Trump presidency, a lawsuit filed in New York by the Democratic National Committee (DNC) claims senior members of the Trump campaign collaborated with the Russian government and its military spy agency in order to help the now-president and hurt his rival, Hillary Clinton. Among those named in the suit are Mr Trump’s eldest son and his son-in-law.

“During the 2016 presidential campaign, Russia launched an all-out assault on our democracy, and it found a willing and active partner in Donald Trump’s campaign,” DNC Chairman Tom Perez said in a statement on Friday morning.

James Comey There aren't enough 'adequate people' in the White House to stop Donald Trump's behaviour

“This constituted an act of unprecedented treachery: the campaign of a nominee for president of the United States, in league with a hostile foreign power to bolster its own chance to win the presidency.”

The civil lawsuit, filed almost 18 months since Mr Trump secured the presidency in a result that surprised most political observers, comes as Special Counsel Robert Mueller is investigating whether there were links between the campaign and Moscow’s alleged meddling in the election. Both President Trump and President Vladimir Putin have repeatedly denied any such interference or collusion.

So far, Mr Mueller has filed charges against four former members of Mr Trump’s team, including former campaign manager Paul Manafort, who has pleaded not guilty to more than a dozen charges. He also brought charges against a Dutch lawyer, 13 Russian nationals and three Russian organisations.

The Washington Post said the lawsuit, which seeks millions of dollars in damages, echoes a similar move enacted by the DNC during the Watergate scandal.

In 1972, the DNC sued former president Richard Nixon’s re-election committee seeking $1m (£714,000) in damages for the break-in at Democratic headquarters in the Watergate building in Washington DC. They eventually won $750,000 (£535,000).

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This time, the DNC is seeking compensation from the various plaintiffs for allegedly hacking the computer networks of the Democratic Party and disseminating stolen material found there, purportedly through Wikileaks.

Wikileaks has never revealed where it obtained the DNC emails that it published on several occasions during the campaign, most notably on the eve of the Democratic Party’s convention in Philadelphia in July – the same day Mr Trump was revealed in an Access Hollywood video from 2005 apparently bragging about sexually assaulting women.

Mr Trump, who has told his lawyers he is prepared to sit and be interviewed by Mr Mueller as he believes he will be cleared by the probe, is not personally named in the suit as a defendant.

Rather, it identifies a series of members of his campaign team who are known to have met Russian officials during the campaign, among them Mr Manafort and his deputy, Rick Gates.

Explosively, it also names the president’s eldest son, Donald Trump Jr, and Mr Trump’s son-in-law Jared Kushner. Both men have denied any wrongdoing, even after it was revealed they took part in a meeting with a Kremlin-linked lawyer at Trump Tower in June 2016, who had allegedly told them she had incriminating material on Ms Clinton.

Mr Mueller already charged Mr Manafort and Gates with money laundering, fraud and tax evasion, in a case brought last year. In February, Gates pleaded guilty to conspiracy and lying to the FBI, and is cooperating with investigators. Mr Manafort has pleaded not guilty.

The DNC lawsuit also names the Russian military intelligence service, the GRU, as a defendant, which has been accused by the US government of orchestrating the hacks, as well as WikiLeaks, and the group’s founder Julian Assange.

The lawsuit was also filed against Roger Stone, the long-time ally of Mr Trump who said during the campaign that he was in contact with Mr Assange.

The Post said the lawsuit contained previously undisclosed details, including the specific date when the Russians allegedly breached the DNC computer system: 27 July 2015.

According to forensic evidence cited in the filing, the party’s system was breached again on 18 April 2016 and, the hackers began siphoning documents and information from DNC systems on 22 April.

The suit notes that four days later, Mr Trump’s then foreign policy adviser George Papadopoulos was informed by Josef Mifsud, a London-based professor, that the Russians were in possession of thousands of emails that could be damaging to Ms Clinton. Papadopoulos has pleaded guilty to a charge brought by Mr Mueller of lying to FBI agents.

The first release of the DNC emails on the eve of the party’s conference revealed that members of the supposedly neutral committee had been working to help Ms Clinton’s campaign, and damage that of her primary rival, Senator Bernie Sanders. As the scandal spread, DNC chairwoman Debbie Wasserman Schultz resigned.

Mr Trump was at the time quick to seize on the DNC’s misfortune, urging Russia to hack his rival’s emails and help find thousands of emails that went missing from the personal email server that she improperly used during her time as secretary of state.

“I will tell you this, Russia: If you’re listening, I hope you’re able to find the 30,000 emails that are missing,” Mr Trump said at a news conference in Florida. “I think you will probably be rewarded mightily by our press.”

The White House directed enquiries to the Trump campaign. There was no immediate response from Mr Assange or the Russian government to the lawsuit.

Mr Stone said the lawsuit was based on “a left-wing conspiracy theory”. “NO proof or evidence,” he he told Reuters.

The Trump campaign dismissed the lawsuit as “frivolous”. “This is a sham lawsuit about a bogus Russian collusion claim filed by a desperate, dysfunctional, and nearly insolvent Democratic Party,” said Brad Parscale, Campaign Manager of Donald J Trump for President Inc.