I've got to strongly disagree with Kevin Drum on this one. Drum says that minority obstruction powers in the U.S. Senate, allowing one senator to hold up legislative business, are the equivalent of nullification, the early-19th century theory that a state could negate a law imposed by the federal government. In the case that Drum cites, the outcomes are roughly similar. That is, a Republican senator is refusing to allow the appointment of an Obama administration nominee, essentially shutting down the oversight board to which the nominee was appointed. Yes, this has roughly the same effect as preventing the federal government from enforcing a duly passed law. But the means are very, very different, and that matters.
The filibuster, construed as any form of minority obstruction in the Senate, is legal, subject only to the rules of the Senate, which the Senate may determine for itself. Nullification runs flatly against the supremacy clause of the U.S. Constitution. Just because the outcomes may be the same doesn't make them equivalent. The assassination of federal officers would similarly obstruct the enforcement of federal laws, but that doesn't make it the same thing as filibustering appointees.