Just when I thought we’d have a long weekend without a big news dump, the WaPo published its story revealing Jared Kushner asked Sergey Kislyak to set up a channel of communication with Russia at Russian facilities at a meeting in early December.

Jared Kushner and Russia’s ambassador to Washington discussed the possibility of setting up a secret and secure communications channel between Trump’s transition team and the Kremlin, using Russian diplomatic facilities in an apparent move to shield their pre-inauguration discussions from monitoring, according to U.S. officials briefed on intelligence reports. Ambassador Sergei Kislyak reported to his superiors in Moscow that Kushner, then President-elect Trump’s son-in-law and confidant, made the proposal during a meeting on Dec. 1 or 2 at Trump Tower, according to intercepts of Russian communications that were reviewed by U.S. officials. Kislyak said Kushner suggested using Russian diplomatic facilities in the United States for the communications. The meeting also was attended by Michael Flynn, Trump’s first national security adviser.

That story — and additional details on Kushner’s discussions with UAE — is the big headliner.

But the fascinating detail is that WaPo received an anonymous letter with details of this meeting — and other things that the WaPo suggests it may not yet have confirmed — in mid-December.

The Post was first alerted in mid-December to the meeting by an anonymous letter, which said, among other things, that Kushner had talked to Kislyak about setting up the communications channel. This week, officials, who reviewed the letter and spoke on condition of anonymity to discuss sensitive intelligence, said the portion about the secret channel was consistent with their understanding of events. For instance, according to those officials and the letter, Kushner conveyed to the Russians that he was aware it would be politically sensitive to meet publicly, but it was necessary for the Trump team to be able to continue their communication with Russian government officials. In addition to their discussion about setting up the communications channel, Kushner, Flynn and Kislyak also talked about arranging a meeting between a representative of Trump and a “Russian contact” in a third country whose name was not identified, according to the anonymous letter.

So who could have sent the letter?

First, consider the timing. The letter was sent within a few weeks of the meeting itself. In between the meeting and sending of the letter, these very same reporters got the scoop that the CIA believed Russia affirmatively wanted Trump elected, a scoop that pre-empted the President’s call for a report on Russian tampering in the election. A week later, two of these reporters got another confirmation that John Brennan said the other agencies agreed with him on the view that Putin wanted Trump elected.

The letter also got received a few days after John McCain got a copy of Christopher Steele’s dossier (reportedly on December 9), followed just four days later by the last known and by far most incendiary installment of the dossier, which for the first time accused Trump’s campaign of paying the DNC hackers.

In other words, WaPo received the letter at a time when the IC was dumping a ton of information implicating Trump. So perhaps it was a spook who heard Kislyak’s description of the meeting on an intercept.

The dominant narrative on those intercepts, however, has said that the IC wasn’t listening closely to Kislyak intercepts until after Russia did not retaliate in response to the hacking sanctions imposed on December 28, and didn’t find the incriminating Mike Flynn conversations until around January 3. If that’s right, then the IC wouldn’t have heard about this meeting until weeks after the letter was sent. [Update: the NYT version of this–which appears to be damage control from the White House–cites a senior American official stating that they learned about this conversation “several months ago,” which would put it after the letter was sent.]

Of course, with the FBI and CIA getting their own raw feeds of data, it’s possible one agency listened to the intercepts (and had the language skills to understand them) before another did. It’s possible, for example, CIA learned about the meeting before FBI did so in the aftermath of the sanctions concerns.

It’s also possible that the Russians sent the letter — or even that Kislyak made up the Kushner claim as disinformation (remember, by this point there were leaks about FISA orders, with reports that Russian interlocutors were changing their communication habits). But it’s unclear what Russia would have to gain by sending a letter in December, rather than waiting until Kushner had compromised himself. Doing so would eliminate all the control they had gained with the information.

Which (barring a spook sending the letter) would seem to leave a Trump associate. Reportedly, WaPo’s Miller said that the letter appears to come from someone inside the Trump transition. Anyone else at the meeting would seem to be an immediate target for Trump retaliation. Though it is possible that Mike Flynn sent the letter, realizing he was getting set up by Trump, which would make the delay in reporting this detail rather interesting. That said, he would have little reason to do so in December, as opposed to now, given that he faces criminal investigation.

Outside of Flynn, though, it’s not clear many people knew this meeting ever happened, much less what happened in it. The meeting was first disclosed by the New Yorker, following which the White House quickly added (in a story to the NYT) Flynn to the story — suggesting he, and not the President’s son-in-law suggested the communication channel.

Michael T. Flynn, then Donald J. Trump’s incoming national security adviser, had a previously undisclosed meeting with the Russian ambassador in December to “establish a line of communication” between the new administration and the Russian government, the White House said on Thursday. Jared Kushner, Mr. Trump’s son-in-law and now a senior adviser, also participated in the meeting at Trump Tower with Mr. Flynn and Sergey I. Kislyak, the Russian ambassador. But among Mr. Trump’s inner circle, it is Mr. Flynn who appears to have been the main interlocutor with the Russian envoy — the two were in contact during the campaign and the transition, Mr. Kislyak and current and former American officials have said. [snip] “They generally discussed the relationship and it made sense to establish a line of communication,” Ms. Hicks said. “Jared has had meetings with many other foreign countries and representatives — as many as two dozen other foreign countries’ leaders and representatives.” The Trump Tower meeting lasted 20 minutes, and Mr. Kushner has not met since with Mr. Kislyak, Ms. Hicks said.

It later became clear that Kushner hadn’t even shared that meeting with White House staffers (presumably including Don McGahn) when responding the Mike Flynn firing, much less included them on his security clearance form.

The extent of Mr. Kushner’s interactions with Mr. Kislyak caught some senior members of Mr. Trump’s White House team off guard, in part because he did not mention them last month during a debate then consuming the White House: how to handle the disclosures about Mr. Flynn’s interactions with the Russian ambassador. Ms. Hicks said that Mr. Trump had authorized Mr. Kushner to have meetings with foreign officials that he felt made sense, and to report back to him if those meetings produced anything of note. She said that because in Mr. Kushner’s view the meetings were inconsequential, it did not occur to him to mention them to senior staff members earlier. “There was nothing to get out in front of on this,” she said.

So there wouldn’t be that many transition staffers who would know of the meeting by mid-December.

That said, one person who knew about the meeting ahead of time was Marshall Billingslea, who tried to warn Flynn about Kislyak. And his request for the Kislyak profile would have alerted the CIA to his concerns about the meeting.

In any case, there are now reports of still more Kushner communications with Kislyak coming out, going back to April 2016. So the FBI sure has a lot to review.

Update: As others have pointed out, at 8:30 there’s a more detailed description of the typed letter, received December 12.