A landmark, Webster's New Collegiate Dictionary tells us, is “an event or development that marks a turning point or a stage.” In my life, the case of Dennis v. United States1 is a landmark, or perhaps more accurately, a series of landmarks. My 1973 doctoral dissertation was on Dennis.2 Four years later that thesis became my first book.3 My second book, a collection of articles on American political trials that appeared in 1981, contained an essay by me on Dennis.4 By then, I assumed, I had said about everything I had to say on the case. In 1993, though, Mel Urofsky brought me back to it, asking me to write a retrospective article on Dennis for the Journal of Supreme Court History, of which he had just become the editor.5 Now, fifteen years later, here we are together again. I am beginning to think that the “grave and probable danger” test that Dennis introduced into constitutional law will be inscribed on my tombstone.