This has been a really important week in the United States Senate, as important a week as we’ve seen there in a long, long time. No, not because Harry Reid out-pokered Mitch McConnell on the filibuster fight. No, not because President Obama finally got some long-scuttled nominees approved on bipartisan votes. No, not because John McCain decided to become, for a while at least, the mavericky McCain of the 1990s and early 2000s. And no, not even because of the bipartisan (did I really use that word twice, to describe the Senate?) deal to keep student-loan rates low, on which they’ll vote next week. Rather, it was a really important week because of the upshot of all those things, or the reason they all happened: this is the week that Mitch McConnell lost his iron grip on the Senate Republican caucus.

That McConnell has had that grip is beyond question, I trust you’d agree. When people like Olympia Snowe (now retired) and Lisa Murkowski (effectively thrown out of the party by Alaska’s voters) vote no on virtually everything, as they did for the duration of Obama’s term, when major items on the president’s agenda (jobs bill, infrastructure banks, etc.) can’t even get a hearing, let alone a vote ... well, it’s not entirely provable, but Senate watchers all know there is only one reason for that: the opposition party’s leadership is basically telling senators, “You vote for X, and I can’t protect you if someone decides to primary you.” That’s a McConnell deal straight up and down.

There were a few, very few, exceptions on high-profile votes. Four Republicans actually voted for the Dodd-Frank bill. There was the fiscal-cliff vote, when, in the late innings, even Fox News hosts were warning Republicans about the polls showing clearly that Republicans would shoulder the bulk of the blame if the government went over the cliff. Even McConnell voted for that one.

But fundamentally, it’s been no, no, no, no, and no. And it’s been because of McConnell and his infamous pledge to make Obama a one-term president.

And suddenly, this week, that changed. How?

In the first case, it was the filibuster showdown that Reid forced. I hope it sunk in on all the Democrats what power they gained from having 51 votes to change those rules, and from the fact that McConnell and all the Republicans knew they had the votes. Just look at what’s happened since.

The first vote was a cloture vote (60 yeas needed) to make Richard Cordray the official head of the Consumer Financial Protection Bureau, an agency the Republicans detest. He passed cloture 71–29, with 16 Republicans voting yea. Trust me: a GOP caucus over which McConnell retained full control would have given Cordray exactly the number of votes needed, five, to clear the cloture hurdle. But 16 of them voted to pass him through (McConnell, of course, not among them).

Then came Cordray’s official confirmation vote, which needed only a 51-vote simple majority. He needed no Republicans, in other words. A GOP caucus listening to its leader would have given him none. He got 12. One of the dozen, Lindsey Graham, later said: “Cordray was filibustered because we don’t like the law. That’s not a reason to deny someone their appointment. We were wrong.”

It continued. Fred Hochberg, the nominee to head the Export-Import Bank, got 82 votes for both cloture and confirmation. Tom Perez for Labor and Gina McCarthy for the EPA were tougher votes for Republicans than Hochberg, but even they made it. Perez didn’t get any GOP votes on confirmation, but he got the six he needed for cloture. McCarthy got 16 Republicans for cloture, including, incredibly, Jeff Sessions and David Vitter. Then she got six Republicans for confirmation.

At this point some liberals will say that wins on matters this routine, the confirmation of people who in the past would have been confirmed with no fuss, are nothing to celebrate. I get that, on one level. But it’s way too blithe a conclusion about what just happened here. The fact is that we’re in the situation we’re in, where Republicans have been at zero. And to go from zero to 5, 12, and 16 is astonishing. And their leader, McConnell, voted no all eight times.

It gets more delicious. At a meeting of Republicans Wednesday, as McConnell tried to argue that he could have gotten a better deal out of Reid without McCain’s intercessions, Bob Corker of Tennessee said “bullshit!” loud enough for people to hear. (Corker, who is certainly a conservative but has often shown signs of wanting to be a real legislator, voted “yea” seven out of eight times, the exception being Perez’s confirmation.) The next day, asked if he would apologize, Corker said he was “glad that that occurred.”

Now McCain vows that he is going to step into a leading role in talks that are coming around soon on the budget, with another debt-and-deficit showdown looming this fall. This is pretty clearly him telling McConnell, you aren’t making all the rules anymore. McCain may have been a little frosted over the immigration issue, which he obviously felt strongly about and on which McConnell again voted no and said absolutely nothing and displayed no leadership at all.

I don’t want to make too much of all this. McConnell’s leadership isn’t threatened. He faces reelection next year—he may yet get a primary opponent from the right, and he already has a strong-on-paper Democrat challenging him in the general election, so his colleagues will give him leeway. McCain’s maverick posture will return, it seems, but probably only occasionally. And they’re still a bunch of hard-shell conservatives, so it’s not as if they’re going to start passing carbon-tax bills.

Even so, this is big and potentially seismic stuff. Remember when Tea Party GOPer Richard Mourdock beat old bull Dick Lugar in a primary in Indiana? That was just last year. At that point, all the Republicans (who weren’t Tea Partiers) were terrified of “being Mourdocked.” Now, a mere year later, they—some of them; enough of them—are concerned about being tagged as too Tea Partyish. Some of them actually want to govern a little—Corker, Lamar Alexander, Mark Kirk, Susan Collins, Jeff Flake, a few others—and are sick, maybe, of blocking everything. And finally, this week, they saw that they can be something other than totally obstructionist, and the world will still spin.

So, again, I hope the Democrats in the Senate take note of the dominoes that are tumbling here because they stood together. And I hope Obama is learning the right lesson here. It wasn’t conciliation and pleas to reason together that forced this change. It was muscle.