It was the eve of a series of votes to end GOP filibusters of seven presidential appointees, and Democrats had vowed they would resort to the "nuclear option" and get rid of such filibusters altogether should any of those stalled nominees remain blocked.
All but two of the Senate's 100 members squeezed into the camera-free old chamber that the Senate used until just before the Civil War. Behind closed doors, they talked for more than three hours.
I buttonholed West Virginia Democrat Jay Rockefeller as he stepped out of that Monday night meeting.
"Senator, is there any kind of a deal?"
"No, there's no deal, but there's a much better understanding."
And that "better understanding" likely did bring about a deal the next morning. In it, a group of Republicans would supply enough votes for the 54-member Democratic caucus to attain a 60-vote supermajority and shut down GOP filibusters of the seven Obama appointees.
In return, Democrats dropped their threat to unilaterally change Senate rules and strip the GOP minority of its right to filibuster executive branch nominees.
"We saw the Senate at its best, when reasonable people from both parties were willing to come together and find common ground," said New York Democrat Charles Schumer, who helped swing the deal. "That's how the Senate should work. That's the way things get done."
In reality, says Rutgers University Senate expert Ross Baker, while Democrats had the votes they needed to change the rules on the filibuster, they also knew doing so could actually make things even worse.
"I think it was a real dread that the atmosphere in the Senate although to outsiders looks terribly poisoned, in actuality, there's a lot of cooperation that goes on under the radar and that had the' nuclear button' been pushed, I think even that level of cooperation would probably have diminished," said Baker.
The end result, says No. 2 Senate Democrat Dick Durbin of Illinois, was that while none of the rules changed, that still remains a possibility.
"What we basically said is we still have our rights to change the rules, if things go to the extreme," explained Durbin. "And the other side has the right to take them to the extreme. But I think we both came to realize Monday night it wasn't in our best interest."
Arizona Republican John McCain led GOP efforts to avert the nuclear option; he's confident it's off the table, at least for now.
"People walked to the edge of the abyss and then we've walked back, so I don't think this is going to come up again anytime soon," said McCain. "It may, depending on what goes on in the Senate."
Like other Republicans, McCain is still willing to block nominations; he put a hold this week on the re-nomination of Army Gen. Martin Dempsey as chairman of the Joint Chiefs of Staff.
Missouri Democrat Claire McCaskill expects a 60-vote supermajority will still be needed for just about anything the Senate does.
"There's still room for bad behavior," she said. "There's room for the Republicans to say, 'We're gonna, you know, require 60 on motherhood and apple pie.' And there's room for the Democrats to say, 'You're not gonna get any amendments, and we're gonna change the rules.' That's all still out there."
Alaska Republican Lisa Murkowski shares such skepticism.
"We got through this week. And that's good," she said. "But I think there are many on both sides who are looking at ... where we are today and saying, 'Yeah, I'm not so good with it.'"
The problem, says Idaho Republican Jim Risch, is that a polarized Senate reflects a polarized nation
"Until the country makes a decision which way they're gonna go, and I don't mean by a 51-49 [percent margin], I mean by a cultural shift, I mean by a 60-40, I think there's going to continue to be polarization. There's gonna continue to be frustration in America."
And likely in the Senate as well.