Cohen has directly implicated Trump in a series of campaign finance violations in 2016, saying that the then-Republican nominee for president, known in court documents as "Individual 1" told him to pay hundreds of thousands of dollars to two women, Stormy Daniels and Karen McDougal, to keep them quiet about affairs he had with them in the 2000s.

Michael Cohen was Donald Trump's lawyer but not the way it is commonly understood - Cohen was the deal guy for the Trump empire, the knockoff version, the US president's keeper of secrets and second in that department only to the Trump brood of children from various marriages.

"This is the beginning of the end for this president. Cohen is deeply hurt and angry and therefore dangerous", says at least one person who has met with Cohen in the last month.

Much of the storyboard is well known. Michael Cohen says wants to shine a light on the darkest alleys of Trumpworld. The White House will paint him as a liar and by the time the dust settles, it will be time for Cohen to serve jail time. Despite the du jour flavour, the Cohen testimony comes close to the John Dean moment from the Nixon era.

John Dean, Richard Nixon's White House counsel, testified against Nixon during the Watergate hearings and broke with Nixon before the last days of that presidency. Michael Cohen was much more involved in the day to day activities of Donald Trump and much higher in the food chain than John Dean ever was in the Nixonian org chart. Michael Cohen has testified in Congress earlier but those details were kept under wraps by Republicans before Democrats stormed back to power in the midterms and took the House majority. Cohen's is merely an early testimony in a long parade of similar ones we'll see all year. Cohen's lawyers have said he is ready to give a "full and credible account" of working for Trump, which is shorthand for running the dirty tricks department.

What Michael Cohen is going to say under oath beginning 26 February is what we are missing so far, despite all of the disparate Mueller filings: What really happened? How involved was Trump in dealings with Russian operatives offering dirt on Hillary Clinton? Was he detail-oriented or disorganized? "He's going to talk about what it was like working with a man (Trump) who has no ethics whatsoever and lies", Cohen confidante and advisor Lanny Davis said on MSNBC. Former Trump organization staffers are saying Trump has lost all his leverage and facing the same troubles in court that he used to put his opponents through - run them dry with long drawn court cases.

What Michael Cohen is going to say to the Congress is as big as the Mueller report simply because we don't know how much of the Mueller report will finally be available to the American public and the world. Cohen is a central witness in the Russia probe investigations and was directed by Trump to have direct contact with the Russians. Cohen has also spent more than 70 hours briefing Robert Mueller's investigators. For someone who said he'd "take a bullet for Donald Trump", Cohen has turned the gun on the US president.