Adam Winkler is a professor at UCLA School of Law and the author of Gunfight: The Battle over the Right to Bear Arms in America.

As political theatre, Senator Rand Paul's marathon, 13-hour filibuster to protest the Obama administration's dreadful drone policy was gripping. While filibusters have become commonplace these days, they usually only involve a simple notice that one intends to filibuster, which then puts the onus on the other side to round up the 60 votes for "cloture" to end the threat. Paul, however, chose to filibuster the old-fashioned way, by standing on the Senate floor and speaking, as Paul said, "until I can no longer speak." While Paul's valiant protest captured the attention of the political twitterati and evoked comparisons to the classic Jimmy Stewart filibuster film, Mr. Smith Goes to Washington, it raised an important question few people were asking: Is the filibuster unconstitutional? 

Surely not, you say. There's something quintessentially American about the lone dissenter, standing up for core principles of due process and the rule of law. Even the mighty Senate cannot silence his voice. The filibuster represents the best of American constitutionalism: protecting political minorities against the aggressive power of the majority. After all, how in the world could Jimmy Stewart be unconstitutional?

The answer, however, isn't quite so clear. While many people might assume that the filibuster is provided for in the Constitution, that document doesn't refer in any way to the tactic. The first Congresses did not have nor recognize a filibuster. Senators had the option of invoking a "previous question" motion, which by majority vote would end debate on whatever topic was being discussed. When that type of motion was eliminated in 1806, the reform wasn't intended to create the filibuster; it was, instead, instigated by the presiding officer of the Senate who thought the previous question motion wasn't needed in a house comprised of "gentlemen" who'd know when to move on. According to one historian of the filibuster, "Far from being a matter of high principle, the filibuster appears to be nothing more than an unforeseen and unintended consequence" of this house-keeping revision of the Senate rules....