The idea that Mr. Manafort’s indictment vindicates Mr. Trump also ignores how complex criminal investigations typically proceed, and the attendant peril Mr. Trump now faces. In our half century of collective experience prosecuting and defending criminal cases, we have watched repeatedly as prosecutors charged lower-level individuals with readily provable offenses that are distinct from the core conduct and targets that are the primary focus of the prosecutor’s investigation.

It’s also significant that Mr. Mueller threw the book at Mr. Manafort and Mr. Gates. Because the federal sentencing guidelines recommend a significant prison sentence for money-laundering offenses and are largely driven by the dollar amounts involved in the crime, this indictment, which involves millions of dollars, puts tremendous pressure on them to make a cooperation deal with the special counsel’s office to try to reduce the lengthy prison sentences each could face.

The power of this “squeeze play” approach is demonstrated by the other filing released today, reflecting a guilty plea by George Papadopoulos, a former Trump foreign policy adviser who admits to communications with foreign individuals during the campaign, including at least one about the Russians’ possessing “dirt” concerning Hillary Clinton “in the form of ‘thousands of emails.’ ” Mr. Papadopoulos lied about these engagements when questioned, and was caught doing so. When confronted with the prospect of jail time, he decided to cooperate. His statements constitute yet another troubling quantum of evidence that the Trump campaign may have known about and encouraged the Russian intrusion on our elections — so-called collusion.

The Papadopoulos plea was finalized this month, and it’s no coincidence that Mr. Mueller held off announcing it until today. It’s a clear signal to Mr. Manafort and Mr. Gates about how they should proceed — and how much the special counsel wants them to. Mr. Manafort was privy to the inner workings of the Trump campaign, and he attended the now-famous June 2016 meeting between Donald Trump Jr. and Jared Kushner and apparent Russian emissaries. Should Mr. Manafort cooperate, he would be an important witness as to what those in attendance said about the event before, during and after — and whether Mr. Trump himself was briefed on it.