The walls have suddenly caved in on Donald Trump’s presidency. First came Michael Cohen’s stunning plea agreement, in which Trump’s longtime fixer and trusted legal gun admitted in a federal courtroom in Manhattan that he had committed crimes at the direction of the president. Then, in Alexandria, Virginia, Robert Mueller’s prosecution team notched a big win with the guilty verdict on eight counts reached by the jury against Paul Manafort, Trump’s former campaign manager.

Facing a second federal trial in Washington DC next month, Manafort will be under intense pressure to cooperate with Mueller in order to avoid spending the rest of his life in prison. After the verdict was announced, one of his lawyers said Manafort was “evaluating all of his options”, pointing towards the possibility of cooperation with Mueller.

A third wall crumbled over the weekend, when the New York Times revealed that the White House counsel, Don McGahn, had spent 30 hours providing information to Mueller. On Sunday, the president himself invoked Watergate in one of his fevered tweets. Referring to the man whose testimony led directly to the vote to impeach Richard Nixon, Trump tweeted that McGahn was no “John Dean type ‘RAT’” in a panicked effort to dispute and discredit the Times story.

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After months of relative quiet, during which Trump denounced Mueller’s probe as a “witch hunt” and his supporters spearheaded a concerted campaign to discredit the special prosecutor, everything has suddenly broken Mueller’s way. The past week could go down in history as being just as consequential as the crucial period in the spring and early summer of 1973, when everything caved in on Nixon. It was then that Dean began cooperating with the Senate Watergate committee and Nixon was forced to fire his closest aides, John Erlichman and Bob Haldeman, the architects of the criminal Watergate cover-up. It was downhill from there until Nixon’s resignation on 9 August, 1974.

One of Cohen’s lawyers, Lanny Davis, revealed before Tuesday’s plea deal that he had contacted Dean in order to help Cohen. “I reached out to my old friend John Dean because of what he went through with Watergate, and I saw some parallels to what Michael Cohen is experiencing,” Davis told Politico. “I wanted to gain from John’s wisdom.”

Dean’s testimony was so significant because of his detailed knowledge, as White House counsel, of Nixon’s direct involvement in the criminal Watergate cover-up and his lies about it. In White House conversations with Nixon, which were taped, Dean had direct knowledge of the president’s crimes.

The parallels with Cohen are clear. He said in court on Tuesday that he committed crimes, including making payoffs that constituted illegal campaign gifts, “in coordination with and direction of a candidate for federal office”. In July, Cohen released to CNN a tape he’d made of Trump discussing a cash payment of hush money to Stormy Daniels. He has other tapes, too. And on MSNBC Tuesday night, Davis made clear that Cohen was ready to share all that he knows with Mueller, including that Trump had advance knowledge of Russia’s illegal hacking of the communications of Democratic officials.

Facebook Twitter Pinterest Former Trump attorney Michael Cohen leaves the US federal court in NYC. Photograph: Jason Szenes/EPA

Manafort, if he too flipped on Trump, could provide more crucial information about collusion between the Trump campaign and Russia. He attended the Trump Tower meeting in 2016 with a Russian lawyer offering dirt on Hillary Clinton, with Jared Kushner and Donald Trump Jr.

No one, including White House officials, seems to know exactly what McGahn told Mueller and whether any of his testimony incriminated the president. But he has intimate knowledge about the issues at the heart of any obstruction of justice charges being investigated by Mueller, including Trump’s firing of the former FBI director James Comey and efforts to dislodge senior justice department officials, including the attorney general, Jeff Sessions.

Mueller has other potential crucial witnesses in the former national security adviser Michael Flynn, Trump’s former campaign advisor Rick Gates, and former foreign policy advisor George Papadopoulos, who have all made plea deals.

Cohen has no formal deal yet to cooperate with Mueller, and such agreements usually take shape over months. But in pleading guilty, he went out of his way to implicate Trump in his crimes, which certainly suggests an agreement is likely.

Like Nixon, Trump will try to use the power of the presidency to undercut the special prosecutor and fight an aggressive press corps. He will continue to condemn the Mueller investigation as a witch hunt. But deputy attorney general Rod Rosenstein smartly handed the Cohen case to experienced New York prosecutors, not Mueller’s team, and it will be harder for Trump to demonise their work.

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Trump could also take out his pardon pen. He has already denounced Manafort’s prosecution and defended him as a good man. A Cohen pardon would seem less likely, as have rumors been circulating for months that he would turn on the president – the man Cohen once said he would take a bullet for.

On Tuesday night, the Democratic Senator Ron Wyden warned Trump that any attempt to buy the silence of his men with pardons would constitute “high crimes and misdemeanors”.

I vividly remember the spring of 1973, when Dean turned against Richard Nixon. I spent most of that June with my ear attached to a transistor radio, listening to his fateful Senate testimony. Once he revealed what he knew, including his unforgettable description of “a cancer on the presidency”, Nixon’s days were numbered.

Michael Cohen has not yet publicly disclosed all that he knows. Worried that he faced arrest for bank fraud and federal campaign finance violations, he reportedly agonised over the weekend before deciding to plead guilty. His stunning admission that his illegal acts were “at the direction of a candidate for federal office” were every bit as shocking as Dean’s words were more than 40 years ago. Back then, as now, the president’s men face stiff jail sentences.

The cancer in Trump’s presidency began during his 2016 campaign, as Cohen and Manafort may help to prove. It has metastasized to his White House. The cure, as was true in Nixon’s time, may involve impeachment.

• Jill Abramson is a political columnist for the Guardian