Michael Cohen began working for President Trump as his personal attorney over a decade ago, well before Trump was seriously considering running for president — back, in fact, when Trump was still a Democrat. Cohen’s role at the Trump Organization was broad, involving him in potential real estate projects and serving, in the New York Times’s phrasing, as a “do-it-all fixer” — a role that apparently included occasionally berating journalists on Trump’s behalf.

During 2016, Cohen did not work directly for the Trump campaign, though he was still working as the candidate’s attorney and making television appearances on behalf of Trump’s candidacy. During the primaries, he was involved in a Trump Organization effort to build a new tower in Moscow. This effort included personal outreach to the spokesman for Russian President Vladimir Putin aimed at speeding the process. (The project was abandoned in mid-2016.)

In late October 2016, with days left before the election, Cohen arranged a payment of $130,000 to adult-film actress Stormy Daniels, preventing her from telling the media about an alleged sexual encounter between her and Trump a decade before. After the election, Cohen pitched himself as a consultant offering insight into Trump and the Trump presidency. He took in millions in consulting fees from a number of corporate and private interests — including the U.S. affiliate of a company founded by a Russian oligarch and, the BBC reported last month, allies of the president of Ukraine.

Here's a breakdown of the people that President Trump's lawyer Michael Cohen has dealt with and the investigations he's entangled in. (Jenny Starrs/The Washington Post)

Cohen is mentioned in the dossier of material compiled by former British intelligence officer Christopher Steele as a liaison between Russian actors and the campaign, claims that have never been validated publicly. Special counsel Robert S. Mueller III is reportedly investigating a visit by Cohen to Prague in 2016 — a trip that would match a detail of the Steele dossier. Mueller is also reportedly looking into a Russia-Ukraine peace proposal that was given to Cohen by a Ukrainian lawmaker and which Cohen gave to then-national security adviser Michael Flynn shortly before Flynn resigned.

Before he worked with Trump and extending into his tenure as the future president’s attorney, Cohen had his own businesses on the side, including owning a number of New York City’s once-lucrative taxi medallions and serving as an adviser to disparate organizations. He also made his own real estate transactions on the side, some of which involved big profits in a short time frame. It’s these efforts, it seems, which resulted in federal investigators working for the U.S. attorney’s office in Manhattan to raid Cohen’s homes and office in April, seizing numerous physical documents and electronic devices looking for evidence to bolster potential criminal charges against Cohen.

At least, that’s what Trump argues.

“This doesn’t have to do with me,” he said about Cohen’s legal troubles during an interview on “Fox and Friends” in April. “Michael is a businessman. He’s got a business. He also practices law. I would say probably the big thing is his business, and they’re looking at something having to do with his business. I have nothing to do with his business.”

That may be the case. It may be true that the acts under investigation are solely related to Cohen’s side hustles. Until charges are filed, if charges are filed, we won’t know.

But it doesn’t really matter. If there are criminal charges in the offing (which seems likely) and Cohen is worried about a conviction (also likely), it gives authorities a powerful carrot to dangle in front of him: cooperation. And Cohen cooperating with the authorities — specifically, with Mueller and his team — is probably the biggest threat that Trump might face.

On Wednesday, multiple outlets reported that Cohen was considering cooperating with prosecutors, having parted ways with the legal team that had been representing him in an ongoing legal dispute over the material seized in that April raid. Cohen is reportedly in a difficult position. He reportedly needs new attorneys, per the New York Times, in part because he has unpaid bills with his representation — the sort of thing that might disincline a law firm to take him on as a client. Or he can reach an agreement with prosecutors to tell them what he knows in exchange for quickly wrapping up the investigation into him.

There are others who could provide a sweeping overview of Trump’s activity before, during and after the campaign, certainly. But the combination of dealing with Trump in all three of those phases, being involved with Trump to the extent that Cohen was and facing possible criminal charges that might inspire someone to flip? Only Cohen fits that bill. Former campaign chairman Paul Manafort no doubt has a lot to offer prosecutors, should he decide to trade in his knowledge for a clean criminal slate. But Manafort can’t speak to the Trump Organization before 2016. He can’t talk about attempts to curry business in Russia before and after the 2013 Miss Universe pageant in Moscow. It’s quite possible that no one except Trump has as broad an overview of Trump the businessman and Trump the candidate as Cohen.

Cohen is also uniquely positioned as a threat to Trump on the campaign. We can set aside the Steele dossier allegations which, if proved true, would be game over for the question of collusion. Consider just the payment to Daniels. It’s not as intriguing as Russian collusion, but it’s quite likely that campaign finance laws were broken by concealing a payment meant to aid Trump’s election. There may be other instances of Cohen fixing similar problems for Trump in 2016 that raise similar questions.

The only two people who know precisely the ways in which Cohen might implicate Trump are Cohen and Trump — though it’s a safe bet that a few people carrying badges around Washington have a good sense of it, too. Cohen’s legal problems may, in fact, be entirely separate from Trump. But if they aren’t, and if Cohen decides to share what he knows with the authorities, it’s hard to imagine someone who is more likely to put Trump at significant legal risk.