Senate Majority Leader Harry Reid pushed that big red button and launched the Democrats' nuclear attack against the United States Senate. By which we mean that, in a 52 to 48 vote, the Senate passed a long-threatened change to its voting rules in order to ease the approval of presidential nominees. Several Democrats voted against the move, but: KABOOM.

That rules change, the much-discussed "nuclear option," was not an insignificant move for Reid. The effects are not as bad as what happened in, say, Hiroshima in 1945, but it upends a long-standing tradition in the chamber. The problem in the Democrats' view, as we've noted before, is that the Republican minority has consistently blocked administration nominees with the filibuster — a rule that requires 60 votes to overcome in a chamber where Democrats hold a 55 vote majority. Over recent weeks, Republicans have blocked three nominees from President Obama (these three) to fill vacant positions on the D.C. Circuit Court of Appeals, a court that hears challenges to broad swaths of federal legislation.

Speaking from the Senate floor on Thursday morning, Reid noted that nearly half of the nominee filibusters in history occurred under Obama. He declared that, "the American people are fed up with this kind of obstruction and gridlock," Prior to the "nuclear option" vote, Reid asked that the body reconsider the filibuster on one of those judicial nominees — in the words of Politico's Burgess Everett, "daring" the Republicans to block her nomination yet again.  They did. In the final procedural vote, Reid himself cast the deciding 51st vote for the change — which, it's important to note, only lowers the bar on non-Supreme Court appointments.

Senate Minority Leader Mitch McConnell argued that the Democrats only wanted to change the topic of Obamacare. "I'd want to be talking about something else, too, if I had to defend dogs getting insurance while millions of Americans lost theirs," he said — but it wasn't enough.

Update, 2:00 p.m.: President Obama issued a statement in support of the move, saying that "neither party has been blameless for these tactics." But, he continued:

Today's pattern of obstruction isn't normal. It's not what our founders envisioned. A deliberate and determined effort to obstruct everything — no matter what the merits, just to refight the results of an election — is not normal.

At The Washington Post, Ezra Klein outlined why the option was finally exercised after being threatened repeatedly. First, the Democrats didn't have any other way to get Obama's nominees moved forward. Second, Democrats felt like they'd already gone far enough in trying to make a deal with the Republicans.

It's hard to overstate the pride senior Senate Democrats took in cutting their January deal with Senate Republicans. That kind of good-faith dealmaking, they said, was exactly how the Senate is supposed to work. Some even argued it was a sign that immigration reform, gun control, and other top Democratic initiatives might pass.

But then Republicans filibustered more judges and executive-branch nominees. And the pride top Democrats took in their deal to avert filibuster reform has turned to anger that Republicans made them look like trusting fools.

And third: Democrats were confident that the Republicans, given the opportunity, would gut the filibuster rules to their advantage. In fact, the term "nuclear option," meant to suggest that the rules change would devastate the ability of the Senate to work together, was coined in 2003 by The Washington Times, following an interview with Republican Sen. Trent Lott. Lott was hoping to warn Democrats that his party might enact a similar rules change. Now, the tables have turned.

The idea of the Republicans regaining control of the Senate was a key reason Democrats were skeptical about the rules change. The Post quotes Iowa Sen. Chuck Grassley: "If [Reid] changes the rules for some judicial nominees, he is effectively changing them for all judicial nominees, including the Supreme Court." Grassley's previously threatened that if the Senate regains the White House and Senate, they could force through Supreme Court nominees hated by the Democrats.

But as NBC's Mark Murray points out, that's a big if. Even if the Republicans win in 2016 and a Republican takes over the next year, that president would have to hope that the Republicans managed to hold a Senate majority in the 2016 races, when Republicans have to defend the vast majority of contested seats. That's not a gimme.

Two of the three Democrats that balked — West Virginia's Joe Manchin and Arkansas' Mark Pryor — represent largely conservative states. The third, Michigan's Carl Levin, has long opposed the idea of changing the rules. 

So the final vote: 52 to 48.