My understanding is that, in modern times, they have something of a protocol to threathen to perform a filibuster and thereby avoid actually needing to do the deed. Of course, they can't make the threats too often, or perhaps, the leadership party may choose to violate the tradition of letting the minority leader run for re-election unopposed, and then manage to bump him out of office. Which, more or less, is what happened to Tom Daschle.