Tieless and looking as if he had just woken up, Donald Trump stepped off Air Force One at about 5:45 on Wednesday morning, following a long flight back from Singapore, where he met with Kim Jong Un, the North Korean dictator. He didn’t enjoy much of a welcome home. Later in the morning, ABC News reported that Michael Cohen, his personal lawyer and fixer, who is at the center of a probe by the U.S. Attorney’s Office for the Southern District of New York, was parting ways with his legal team and was “likely to co-operate with federal investigators.”

The ABC News report sparked a media frenzy, and numerous further reports. The Wall Street Journal reported that Cohen’s current lawyers, who are from the Chicago-based law firm McDermott Will & Emery, were quitting, and said Cohen “wants to hire a lawyer with close ties to the Manhattan U.S. Attorney’s office.” The Times said there was an issue about “the payment of legal bills.” Vanity Fair’s Gabriel Sherman tweeted, “Person close to Cohen says he hasn’t flipped yet, he’s sending up a smoke signal to Trump: I need help.”

Although some of the details remain vague, a few things are clear. Friday is the deadline that a federal judge, Kimba Wood, set for an independent law firm to sort through the materials that the F.B.I. seized from Cohen during a dawn raid, in April, on his office, home, and hotel room, and to decide which are covered by attorney-client privilege. Once the sorting process is completed, investigators from the U.S. Attorney’s office will gain access to the material that isn’t privileged, which may well include many of the contents of Cohen’s cell phones, computers, and filing cabinets. Many legal observers believe that an indictment of Cohen is likely to follow pretty soon. That’s partly because the feds are widely assumed to have presented evidence of probable wrongdoing to obtain the warrant they used to raid Cohen’s properties.

Second, we know that Cohen’s legal bills are mounting. In a recent court hearing, one of his lawyers said, “We have people working all night. We have people sleeping on couches in our offices. We have people who worked all through the Memorial Day weekend.” In addition to paying his own bills, Cohen has also been obliged, by Judge Wood, to pay up to half of the bills from the legal team that sorted through the seized materials. Since Trump was elected, Cohen has made quite a bit of money by selling his services as a “consultant” to big corporations and an investment firm tied to a Russian oligarch. But he doesn’t have the sort of wealth that could enable him to be oblivious to the mounting cost of his defense.

Thirdly, we can be pretty sure that Cohen has at least some information that federal prosecutors, including Robert Mueller, the special counsel, would be interested in hearing, even if it doesn’t directly implicate the President. (If Cohen did make a deal with the Southern District, the things he said would almost certainly be made available to other prosecutors, including Mueller.)

In a useful post on his Just Security blog, on Wednesday, Ryan Goodman, a law professor at N.Y.U. who served in the Obama Administration, pointed out some of the leads that Mueller might be keen to pursue with Cohen.

First, there is the Russia connection. Cohen has extensive links in New York’s business community of Russian-born immigrants. It is well known that he worked with Felix Sater, a Russian-born business associate of Trump, on an abortive project to develop a Trump Tower in Moscow. Sater has said that there was nothing untoward about their efforts. But, according to a lengthy report that Buzzfeed published last month, “FBI agents investigating Russia’s interference in the election learned that Cohen was in frequent contact with foreign individuals about Trump Moscow—and that some of these individuals had knowledge of or played a role in 2016 election meddling.”

Mueller may also be interested in clearing up the issue of whether Cohen visited Prague in 2016, and met with people connected to Russia, as was alleged in the Steele dossier. Cohen has adamantly denied that he visited the Czech capital, although he concedes that he did go to Italy for a week in August, 2016. A couple of months ago, McClatchy reported that Mueller's team has unearthed evidence that Cohen did go to Prague, but that story hasn’t been confirmed by other media outlets.

A third area of interest may be Cohen’s role in pushing a Russia-Ukraine peace plan that was hatched by a Ukrainian politician, Andrey Artemenko, but which reputedly also had the backing of Russians close to the Kremlin. It has been reported that Cohen gave a copy of this plan to Michael Flynn, Trump’s national-security adviser, a week before Flynn got fired because he lied about contacts he had with the Russian ambassador to Washington, Sergey Kislyak.

In another area of concern, Cohen may provide information about payoffs that he made on Trump’s behalf to women who claimed to have had affairs with the President. We know about the payment of a hundred and thirty thousand dollars that Cohen made to Stephanie Clifford (a.k.a. Stormy Daniels), of course. But Rudy Giuliani, Trump’s lawyer and cable-news pit bull, has publicly indicated that it is perfectly possible that Cohen paid off more women before the 2016 election. “I have no knowledge of that, but I would think, if it was necessary, yes,” Giuliani told ABC News, in May.

Finally, there are any other business dealings that Cohen may have been involved in on Trump’s behalf. We don’t know everything Cohen did for Trump, and there were in-house lawyers at the Trump Organization who vetted a lot of the President’s ventures, including the overseas ones. But Mueller would presumably like to hear a full accounting of what Cohen did for his boss.

An earlier version of this post misstated the identity of the client of McDermott Will & Emery