Thus, a rule that one can only use deadly force to defend oneself against threats of death, serious bodily injury, rape, kidnapping, and a few other very serious threats would likely be constitutional (even though many states also allow use of deadly force to defend against robbery and in some situations burglary). Likewise, the “duty to retreat,” which is to say the principle that deadly force can only be used in self-defense if it’s genuinely necessary, in that no safe avenue of retreat is available, is likely to be constitutional, too, because it has long been recognized in at least a substantial minority of states. There may be other examples as well. My point is that a federal constitutional right to self-defense likely exists, especially in the wake of Heller. But it is not unlimited, and is likely to be strongest precisely where there’s a broad and deep common-law and statutory tradition of recognizing such a right.