I have no deep thoughts about this but it’s worth flagging, as reporters who cover the Senate regularly and were there after the briefing ended found it unusual and potentially significant for a number of reasons. For one thing, the briefing was long — close to three hours by one account. It was also secretive even by traditional standards: Although Comey was photographed leaving the meeting, committee members wouldn’t admit that he’d been there. And it seemed as though the briefing was urgent, with senators delaying their departure during a weekend recess to hear what Comey had to say.

What’s going on?

Members of the Senate Intelligence Committee, along with ex-officio member and Minority Leader Charles E. Schumer, huddled for a total of more than two hours on Friday with Comey.

The FBI director’s visit was not announced publicly, and it’s possible members of the Capitol Hill press corps only found out because he was spotted in the hallways and entered a secure room used for intelligence briefings.

But leaving that secure room in the Capitol Visitor Center, senators declined to even confirm the presence of the FBI director, much less the substance of the meeting. Those who did talk generally only gave “no comments” or referred questions to Intelligence Chairman Richard M. Burr and ranking member Mark Warner.

A HuffPo reporter dialed up some Senate staffers afterward hoping for a scoop and got stony silence — except from one, who told her that not even staff were told about the briefing. A Bloomberg reporter on the scene as the meeting let out said the change in the senators’ demeanors afterward was notable:

Hmmm. The Senate Intel Committee considers all manner of intelligence matters so in theory the briefing could have been about anything. Most recently, though, the Committee’s been in the news because it’s leading the congressional investigation into Russian interference in last year’s presidential campaign. Three days ago, after Mike Flynn resigned, Mitch McConnell said he thought it was “highly likely” that the Committee would include Flynn’s interactions with the Russian ambassador as part of its broader inquiry. And now suddenly Comey’s on the Hill, amid unusual secrecy, addressing them in what seems to have been an especially important briefing.

Still, we need more than that to suspect that the briefing was about Flynn, Russia, and/or Trump campaign advisors’ “constant communications” with Russian officials during the campaign. Which … is where Marco Rubio comes in:

He tweeted that yesterday afternoon following the briefing. The word “now” strongly suggests that something that just came to light has convinced him and the rest of the Committee to treat the Russia matter even more gravely than they had before. The word “bipartisan” is significant too, as Democrats were of course already gung ho to investigate. Rubio seems to be suggesting that whatever Comey told them was so serious that Republicans would be eager to get to the bottom of it too. Hmmmmmm.

An open question: Has part or all of Comey’s information leaked to the media, with stories already in the works about the mysterious allegations? It didn’t occur to me at the time that there was anything more to Trump’s tweet yesterday about the media as “enemies of the people” than the president being in one of his peevish moods, but David Frum had some interesting speculation about the possible cause of that peevishness:

That’s just a theory, but if something big is about to drop, the papers may well have already contacted the White House for comment about it, alerting Trump that it’s coming and ticking him off. Could be that Frum’s wrong, of course, or it could be that he’s right but the big scoop has nothing to do with what Comey told the Intelligence Committee. We’ll probably know this week.

Update: Lo and behold, here’s Reuters with a new story this afternoon claiming that Comey’s FBI is running no fewer than three separate investigations into Russian hacking during the campaign. “This counterintelligence inquiry includes but is not limited to examination of financial transactions by Russian individuals and companies who are believed to have links to Trump associates. The transactions under scrutiny involve investments by Russians in overseas entities that appear to have been undertaken through middlemen and front companies, two people briefed on the probe said.”