In the US House of Representatives, majority rules. Any legislation which can garner 50% of the chamber’s votes (plus 1) passes, and there are very few procedural tricks which a minority party can implement to delay or avoid having legislation with which they disagree – or even loathe strongly – passed by the majority. In the Senate, however, it’s an entirely different game. The Senate was conceived as (and is still supposed to be) the elder, more mature and deliberative body, in which legislation which is passed by the more-rambunctious House gets a careful going-over, deeper scrutiny, and is often refined or tempered before ultimately being passed along to the President (or, as is increasingly the case lately, rejected). In theory, Senate votes are supposed to function exactly the same as House votes: 50% plus one vote equals passage. However, the Senate has an additional procedural catch called the filibuster. The filibuster is a part of the Senate rules designed to give the minority party some influence – power – they would not otherwise possess in a simple majority-rules situation (like what exists in the House). It was intended to keep any political party which was able to secure a majority of seats from simply running roughshod and relegating all minority parties to irrelevance because they cannot muster enough votes.
The filibuster works like this: if any Senator so dislikes a particular piece of legislation that not only would they vote against it, but they feel it should not even be debated, they can lodge a filibuster. Initiating a filibuster means that debate on the bill in question cannot be brought to a close. This is important because in order for any bill in the Senate to be vote on, it must be debated fully and then a motion must be made to close debate. The motion to close debate and proceed with the vote on the bill must be agreed to “without objection”. A filibuster is how any Senator objects; how he or she says “I do not agree to close debate on this bill.” The result is that if a filibuster is lodged and thus debate on a bill cannot be ended, the bill is never able to be voted upon, killing it as effectively as if it had been voted down in a normal vote. This is true no matter how many Senators would have voted yes on the bill. And remember, a single Senator can trigger a filibuster.
So is there a way to stop Senators from simply blocking bills they don’t like – even popular ones – through the use of filibusters? Yes: the rest of the Senate can vote to invoke cloture, which is another fancy Senate process term which essentially is a counter-motion to the filibuster. A motion to invoke cloture is a vote to cut off debate anyway. It overrides the filibuster, allowing a regular, simple-majority vote on the original bill to be held. But the catch is that in order to successfully invoke cloture and cut off debate, ending the filibuster, Senate rules require 60 Senators voting yes to pass. What this means in practice is that although the vote on the legislation itself still only requires 51 votes, that vote can never be held once a filibuster is launched. Thus, in order to pass, any bill which is filibustered must effectively have 60 votes in favor in order to shut off debate (and therefore to pass). It is a means by which the minority party in the Senate can change the vote threshold needed to pass any bill they filibuster from the customary 51 to 60 – a much harder level to achieve.
If you aren’t familiar with the filibuster, you might be tempted to think that 60 isn’t that much more than 51…and numerically, you’d be partially right (though 60% is arguably still considerably more than 51% on purely mathematical grounds, even though in the Senate, it’s only a total of nine individual votes). However, it isn’t the increase in number alone which makes 60 more difficult than 51 to achieve, it’s the party politics behind it. America is still, today, pretty evenly divided between Democrats and Republicans. This trend is magnified in the Senate, where every state has the same number of votes: two. That makes teeny-tiny states (population-wise) like Montana or Rhode Island as powerful in the Senate, vote for vote, as enormous ones like Texas, New York or California. States whose demographics are primarily rural (like much of the mountain west: Wyoming, Idaho, etc.) tend to be reliably Republican, and in the Senate, these states cancel out much larger, more populous states, meaning that it’s very difficult – and uncommon – for either party to hold sixty or more seats in the Senate at any time. It does happen, but not regularly.
When it comes to the filibuster, remember: any Senator can launch one…but if a Senator was acting completely alone without the backing of his or her party, they would likely be easily outvoted on the motion to invoke cloture. That’s not how the filibuster works in practice, most of the time. Instead, what happens is that minority parties use the filibuster as I described above. When a Senator launches a filibuster of a particular bill, it’s understood that they are doing so at the behest of their party. That means an observer can reliably count on however many seats that party currently occupies in the house as reliable “no” votes on the cloture motion. So, in practice, that tends to mean that any time a filibuster is launched, if the party launching it has at least 41 seats in the Senate, the motion to invoke cloture will fail the 60 vote threshold, the filibuster will hold (meaning debate on the bill cannot be cut off), and the bill will die without a vote, even if it had as many as fifty-nine Senators who would have voted in favor of it. That’s why it’s considered the best weapon of the minority party: because as long as they have at least 41 seats, any filibuster they launch will likely be successful.
Sometimes, on particular bills, the vote to invoke cloture does not break down so reliably along party lines. Occasionally one or more Senators will cross over the aisle and vote with the other party. But far more often than not, a filibuster divides the Senate along party lines. And that means that if the majority party doesn’t occupy sixty or more seats (very difficult to achieve, which is why they call such a high number a “supermajority”), they usually can’t invoke cloture and defeat a filibuster.