Back in mid-July, I wrote a Fix post headlined "The nuclear option won't be invoked. Not now. And probably not ever."

Five months later, the nuclear option was invoked.  Jon Chait of New York Magazine took to Twitter to remind me of this fact. He tweeted:

So, that happened.

When I am wrong -- and, yes, it occasionally happens -- I like to figure out why in hopes of not being wrong again. So, let's do that.

The July piece was written after Senate Majority Leader Harry Reid (D-Nev.) and Sen. John McCain (R-Ariz.) brokered a deal that allowed a handful of President Obama's nominees -- including for the National Labor Relations Board -- to get votes. My argument was three-fold: (1) in order for the nuclear option to be used, the old bulls of the Senate would have to trigger it. Since the old bulls -- like Reid -- were the biggest traditionalists, I presumed it wouldn't happen; (2) Reid had spent time in the Senate minority and knew that a Senate in which judges and executive branch nominees could be approved by a simple majority vote would badly disenfranchise whichever party is in the minority; and (3) the public doesn't care about filibusters, so why waste political capital trying to change the rules?

Viewed broadly, what I misjudged was that the way politics has always been conducted -- or the way it had been conducted for a very long time -- does not mean that it is the way it always will be conducted going forward. The nuclear option had been used as a threat that both sides knew neither side would ultimately use for much of the last decade. That fact alone, however, did not guarantee it would never be used. The reality is that the Senate (and political Washington more generally) is a different place than it was even a few years ago.

The main reason for that is the massive turnover in the Senate over the past several election cycles. Since 2008, 40 new Senators -- 20 Democrats, 20 Republicans -- have been elected. Six years ago, 44 senators had served at least three terms; today that number is 32. At the start of the 113th Congress, more than half the senators had served one full term or less. All of that turnover has led to huge numbers of senators who simply don't know how the other half lives. There are currently 55 senators who have only been in the chamber as a member of the Democratic majority or Republican minority.

That change in the composition of the Senate means that not only are many of the longtime defenders of Senate tradition gone --  people like Bob Byrd of West Virginia, Ted Kennedy of Massachusetts, Pete Domenici of New Mexico and John Warner of Virginia -- but also that long-timers like Reid face a very different caucus than they once did. Reid had been under pressure for quite some time from younger, more liberal members -- like Jeff Merkley -- to change the filibuster rules but had resisted. But, over time his resistance waned as he realized that changing the rules was actually what his caucus now wanted -- and that they were willing to accept the consequences of their actions when they went back into the minority at some point in the future.

Finally, we misread the fact that people don't care about the filibuster. They don't. At all. But, rather than being a deterrent, that lack of interest emboldened Reid. With the public tuned out to the parliamentary fights of the Senate, there was little political risk -- either personally or more broadly for his party -- for Reid's rule change. Is there any way that Louisiana Sen. Mary Landrieu loses reelection next fall because she supported changing the rule on filibusters of executive branch and judicial nominees? Or Kay Hagan in North Carolina? Or Reid if he decides to run for reelection in 2016? No way.

So, that's that. Lesson learned.