Why did Harry Reid finally, convincingly threaten to go nuclear? After all, Republicans have been obstructing Barack Obama’s nominations since approximately January 20, 2009. And if anything, there’s been somewhat less obstruction this year; the beginning of the session deal seems to actually have been working.

The basic answer is Republican overreach — or, to simplify, Ted Cruz got Richard Cordray confirmed.

The case for filibusters on executive branch nominations is relatively weak to begin with. And not only on the merits. The reality is that both parties have an interest in a well-run confirmation process, with opportunities for individual senators to exercise leverage on issues important to their states. Turning what had traditionally been simple majority confirmation into a 60-vote obstacle was unlikely to work.

Yet judging from the past four years, Democrats weren’t going to go to the mattresses over a small number of those choices — even the “nullification” cases of Richard Cordray and the National Labor Relations Board picks. Nevertheless, over time, Democrats began to push back, culminating in a deal in January.

What what wrong? Republican overreach. The attempt to kill the confirmation of Chuck Hagel — a Republican and, more importantly, a former Senator — was apparently a big part of it. But certainly the treatment of nominees for EPA and Labor, on top of the ongoing nullification filibusters and plenty of others, pushed Reid and other reluctant Democrats to decide that without a confrontation, they would be essentially giving away a significant portion of Obama’s presidency (and their own elections to the Senate).

It’s not just the substance. It’s also style. As Jonathan Chait noted, something happened to “flip the switch in McCain’s brain from ‘Obama Hater’ back to ‘McConnell Hater.’ ” Or, perhaps, Ted Cruz hater. McCain opposed Hagel’s nomination, but criticized some of Cruz’s over-the-top rhetoric at the time, and, as Greg pointed out earlier, he’s been upset with tea party opposition to going to conference on the budget. It’s possible to exaggerate the importance of personal relationships in the Senate, but they’re not irrelevant — and McCain, in particular, has always seemed to be driven by personal vendettas. A little more focus on Obama as a Kenyan socialist and a little less on nutty accusations of treason against Hagel might have gone a long way with the senator from Arizona.

Going forward, what does this suggest? “Real” conservatives — the brand that we’ve shorthanded as “tea party” for the last few years, although there’s really no difference between them and previous generations of radicals in conservative clothing — have always believed that, well, extremism in pursuit of their goals is no vice. Leaving ethics aside, what this episode demonstrates, not for the first time, is that extremism can be a tactical disaster.

Or, to put it another way: If the only Republican goal is to please the relatively small portion of the electorate that responds to Rush Limbaugh and the rest of the conservative freak show, then they’re not going to be maximizing either their electoral or their legislative possibilities. That might be a trade-off that Ted Cruz is happy with. Whether it’s smart for mainstream conservatives, however, is another story altogether.