Nine reasons the filibuster change is a huge deal

2. Well, technically it still applies to all bills and Supreme Court nominations. In practice, legislation that mainly uses the government's tax and spending powers can evade the filibuster using the budget reconciliation procedures. That's how George W. Bush's tax cuts passed, and how Obamacare was finished. As for the Supreme Court, it's very hard to believe that Democrats or Republicans would accept filibusters of qualified Supreme Court nominees, either. And, as Democrats proved today, they don't have to.

3. The filibuster now exists in what you might call an unstable equilibrium. It theoretically forces a 60-vote threshold on important legislation. But it can — and now, in part, has —been undone with 51 votes. Its only protection was the perceived norm against using the 51-vote option. Democrats just blew that norm apart. The moment one party or the other filibusters a consequential and popular bill, that's likely the end of the filibuster, permanently.

4. The practical end of the Senate's 60-vote threshold is not plunging the chamber into new and uncharted territories. It's the omnipresence of the filibuster in recent decades that plunged the chamber into new and uncharted territories. At the founding of the Republic, the filibuster didn't exist. Prior to the 1970s, filibusters — which required 67 votes to break for most of the 20th century — were incredibly rare.

5. As Gregory Koger, a University of Miami political scientist who researches the filibuster, told me: “Over the last 50 years, we have added a new veto point in American politics. It used to be the House, the Senate and the president, and now it’s the House, the president, the Senate majority and the Senate minority. Now you need to get past four veto points to pass legislation. That’s a huge change of constitutional priorities. But it’s been done, almost unintentionally, through procedural strategies of party leaders.”

6. The rise of the filibuster and the death of the filibuster can be traced to the same fundamental cause: Party polarization. Before the two parties became reasonably unified and disciplined ideological combatants, filibusters were rarely used as a tactic of inter-party warfare because each political party had both members who supported and opposed the bills in question. As that era waned, the filibuster became constant because parties could agree on what to oppose. But that's also why the filibuster's days were (and are) numbered: The majority party agrees on what to support, and continual filibusters against those items increase the majority party's anger at the filibuster itself.

7. Republicans take a lot of the blame here. They've used the filibuster more aggressively than Democrats, by a wide margin. They've also been less willing to cooperate with Democrats on general legislative efforts, making the presence of the filibuster more costly to the Democratic Party. And they've been so unwilling to work with Democrats this year that they essentially removed all reason for Democrats to stay their hand. The way Senate Democrats saw it was that if they weren't going to get immigration reform or gun control or jobs bills or anything big that they cared about, then at least they would get their judicial and executive-branch nominations.

8. There's a lot of upside for Republicans in how this went down. It came at a time when Republicans control the House and are likely to do so for the duration of President Obama's second term, so the weakening of the filibuster will have no effect on the legislation Democrats can pass. The electoral map, the demographics of midterm elections, and the political problems bedeviling Democrats make it very likely that Mitch McConnell will be majority leader come 2015 and then he will be able to take advantage of a weakened filibuster. And, finally, if and when Republicans recapture the White House and decide to do away with the filibuster altogether, Democrats won't have much of an argument when they try to stop them.

9. With gun control dead, immigration reform on life support and bitter disagreement between the House and Senate proving the norm, it looked like the 113th Congress would be notably inconsequential. Today, it became notably consequential. It has changed how all congresses to come will work. Indeed, this might prove to be one of the most significant congresses in modern times. Today, the political system changed its rules to work more smoothly in an age of sharply polarized parties. If American politics is to avoid collapsing into complete dysfunction in the years to come, more changes like this one will likely be needed.