First, it is supersedes. Secondly, I don't see how Caetano is really replacing that ruling when it still uses the "bearable arms" mantra without being able to specify what "bearable arms" exactly are. Heller was at least able to say "all commonly used weapons today are bearable arms". It's still ridiculously stupid but at least it's some form of definition. So if Caetano goes over Heller, then the US went basically backwards and has no clear definition of what "bearable arms" fall under the 2nd. Make it make sense?