I noted in the Papadopoulos post this morning that his plea deal says he’s cooperating with Mueller’s investigation. Brad Heath of USA Today made a nifty catch, though, about the possible extent of that cooperation.

According to the plea agreement, Papadopoulos was arrested on July 27 and signed his deal with the feds on October 5, although not until this morning was that publicly known. The court had sealed the files related to the case. How come? This bit, from a motion Heath noticed in the now unsealed case’s file, may explain it:

Mueller's office said in a court filing that Trump aide George Papadopolous "indicated that he is willing to cooperate with the government." pic.twitter.com/NkEqrxFTeI — Brad Heath (@bradheath) October 30, 2017

Heath didn’t say which filing that passage comes from but logically it’s probably from Mueller’s motion to seal. The key phrase is “proactive cooperator.” Toronto Star reporter Daniel Dale asked someone who would know what that phrase might mean:

Papadopoulos is described as "proactive cooperator." Former prosecutor tells me that sometimes means "wore a wire." https://t.co/nQyVCbXy6x — Daniel Dale (@ddale8) October 30, 2017

Jeryl Bier dug around in old court cases looking for the term and came up with this:

So that’s why Mueller wanted to keep Papadopoulos’s arrest a secret. Papadopoulos may have been secretly working for the feds for the past three months, since his arrest, to gather evidence on suspects in related Russiagate matters in hopes of leniency. He was a perfect guy to try to recruit for that — young, in over his head, outside the Trump inner circle and therefore owing little loyalty to the administration. Mueller may have scared him senseless with threats of a long prison sentence for lying to the FBI and the promise of much reduced charges if he played ball. Possibly he enlisted Papadopoulos to reach out to some of the major players in Russiagate and get them on record confessing to … what, exactly? The problem with using Papadopoulos is that presumably he wasn’t a big enough cheese to make a guy like Manafort comfortable with discussing campaign secrets with him in the course of a “normal” conversation between them. He was a low-level guy.

But even a low-level guy might be big enough to get some people on tape encouraging him to obstruct justice. A Democratic senator, Sheldon Whitehouse, promised more to come on that front today:

“This indictment may be beginning of the end for some ultimate targets, but for sure this is the end of the beginning phase of investigation,” Whitehouse said in a series of tweets. “False statement charges (present in this indictment) and obstruction of justice charges will likely figure prominently.”

Imagine Papadopoulos phoning a former top Team Trump official in early August to say, “They’ve arrested me! I don’t know what to do! I think I should tell them everything and make a deal!” He might have been told no, no, no, stay calm, deny X, Y, and Z, we’ll make sure Mueller never finds our emails from the campaign. And meanwhile, unbeknownst to the target, Mueller’s recording the entire conversation on Papadopoulos’s end.

That would also explain that curious WaPo story on August 14 citing various messages sent between Papadopoulos and campaign officials about Russia, all of which seemed to exculpate Team Trump and make it look like Papadopoulos himself was the only one eager to get Trump together with the Kremlin. In hindsight it sure looks like word of Papadopoulos’s arrest in late July had gotten out somehow and someone from the campaign was doing preemptive damage control by leaking to WaPo. But how did campaign staff find out that Papadopoulos had been arrested? One logical possibility: He told them himself in the course of asking for “advice” from them on how to obstruct the investigation, which some of them may have provided. Suddenly those people woke up this morning and realized they’d had conversations with Papadopoulos recently about how to throw Mueller off the trail and only now do they realize he’s been in cahoots with Mueller for three months. Hoo boy.

Update: Reporter Jason Zengerle notes that the FBI has used this tactic before.