When your government is not at all constrained by laws that's tyranny. We all know that wars are to be authorized by Congress. Obama didn't even bother to ask them as he attacked Libya.
Rights of habeus corpus go back hundreds of years, to the Magna Charta. In cases where our government doesn't want to abide by them though these days they are out. What about cruel and unusual punishment? Bradley Manning is being subjected to mind destroying isolation and isn't even convicted yet.
Bush has admitted torturing, which violates laws that are on our books. It's not merely international law that he violated. Seems it doesn't matter. The rules don't apply to top governmental officials. At what point do you call it tyranny?