It is probably Mr. Kushner who is in greatest jeopardy now. Bloomberg has reported that he is the very senior transition member who directed Mr. Flynn to reach out to Russia. Mr. Kushner has already been questioned by the special counsel and by Congress. If he was one of those officials Mr. Flynn spoke to and he was not honest about it when questioned, he could face similar false statement charges.

Mr. Kushner also failed to disclose approximately 100 foreign contacts on his security clearance application; each omission is a potential false statement. Mr. Flynn may have information about conversations with Mr. Kushner that would demonstrate that the omissions on Mr. Kushner’s form were intentional, and therefore criminal. Remember, we do not know everything Mr. Flynn has to say. What was disclosed in the court filings and hearings is probably only the tip of the iceberg; prosecutors generally keep that to the bare minimum needed for the guilty plea, in order to avoid tipping their hand in their investigation.

Donald Trump Jr.’s exposure is also deepened by the Flynn plea, along similar lines as Mr. Kushner. He might (or might not) be one of the unnamed transition participants Mr. Flynn identified. Moreover, the president’s son has been interviewed at length as a part of congressional investigations, and Mr. Flynn’s testimony could show he was not candid. Because of Mr. Flynn’s role on the campaign as a trusted member of the inner circle, he may also have a great deal to say about topics like Mr. Trump Jr.’s June 2016 meeting with several Russians, Mr. Manafort and Mr. Kushner, or about the Trump scion’s contacts with WikiLeaks. If Mr. Flynn’s recollection is not the same as what Trump the Younger told Congress, Don Jr. is in serious trouble.

Finally, Mr. Flynn’s cooperation could also place Mr. Trump himself in real jeopardy. ABC News has reported that Mr. Flynn will say Mr. Trump “directed him to make contact with the Russians.” If that is so, it opens a Pandora’s box of questions for the president. Is that a reference to the calls about the sanctions, or something else? How many times did Mr. Trump do that, when, and about what? How can we square that with the president’s denials of knowledge about the Flynn contact with Sergey Kislyak, the Russian ambassador, or any contact with Russia? The possible answers range from bad to worse to fatal for the president.

Whether or not that reporting is borne out, there are a variety of other ways Mr. Flynn could damage the president. Mr. Trump is said to be under investigation for obstruction of justice. That includes allegedly telling the F.B.I. director at the time, James Comey — in an apparent reference to the very conduct to which Mr. Flynn has pleaded guilty — “I hope you can see your way clear to letting this go, to letting Flynn go.” There is already significant evidence that Mr. Trump obstructed justice, and Mr. Flynn may be able to add to it — for example, by testifying that those efforts came at his request, or by sharing any other relevant conversations he had with the president.