How Robert Byrd Jr. created the modern filibuster

Commenter WoodbridgeVA adds an important piece to the filibuster story:

The major change in Senate rules that made possible the modern filibuster occurred under the leadership of Robert Byrd during his first stint as Majority Leader. Byrd introduced the concept of "dual tracking" under which the Senate could have two or more bills under floor consideration at any one time. Prior to this change, a filibuster ended floor consideration of all other bills until the one being filibustered had been disposed of. No appropriations, no nominations, no unanimous consent agreements, no nothing. All Senate business came to a dead halt during a filibuster, which raised the stakes on the members conducting the filibuster exponentially. The pressure that would be brought to bear if the entire Senate ground to a halt was one of the reasons filibusters were so rare. Once Byrd changed the rules to allow dual tracking, filibusters became almost pain free. A Senator simply had to announce they intended to filibuster and the Majority Leader would use his dual track authority to move to other business and get around the road block. Over time, most leaders simply did a whip check and declined to schedule a bill if a filibuster was possible..

The dual-track authority is a fairly big piece of the puzzle. But the question, in part, is why it's been allowed to stand. Both Hill experts and political scientists argue that the reason, basically, is that the Senate has things to do. The frequency of the filibuster means that ending the dual tracking would be the same as shutting down the government. It would be a high-stakes showdown over a Senate rule change, which is not something that many in the Senate have evinced much interest in attempting.

But this is how the filibuster was normalized into a 60-vote requirement. Byrd responded to the slight uptick in filibusters by making it much easier and cheaper to filibuster, rather than leading a fight to make it much harder to filibuster. But he saw that as streamlining the process. It's not like the minority was going to filibuster everything. It just wasn't done.

But senators of both parties adapted to the new rules. This was still some years before the filibuster became constant, which allowed the Senate to ease into the new regime. But as people began to understand that threatening the filibuster was a lot easier than filibustering, they began to do it more often. The majority and the minority began to think in terms of 60, and strategize in terms of 60. And then, in the '90s and oughts, when the filibuster became the only Senate rule that mattered, it wasn't such a big leap from the period right before that, and so it didn't cause a showdown, either. The story of the filibuster is a story of small changes that everybody got used to, which allowed for more small changes that everybody got used to, and so on, until the Senate had undergone a large change indeed.