Today the Supreme Court held oral argument in Arizona v. Johnson, a Fourth Amendment case on the stop-and-frisk power. You can read the briefs here, and the oral argument transcript is here. At its broadest level, the case raises the question of whether a police can "pat down" a suspect for weapons if the office reasonably believes the suspect poses a danger to him but there is no evidence that there is criminal activity afoot.

  In my view, the broad question in Johnson has a sense of unreality about it. If a police officer reasonably believes that a suspect is about to attack him, either with a knife or gun, then there will almost always be criminal activity afoot. In Johnson, for example, the defendant had just admitted that he was a felon, and the officer had reason to think he was concealing a weapon: Those facts alone justified a reasonable belief that criminal activity was afoot in the form of concealing a weapon (a state offense in Arizona) or being a felon in possession (state and federal). It's true that the officer testified in Johnson that she wasn't subjectively thinking about that, but that's irrelevant: The Fourth Amendment standard is reasonableness, and reasonableness is based on what a reasonable officer observed rather than what the officer was subjectively thinking. See, e.g., Devenpeck v. Alford.

  More broadly, if the suspect is truly armed and truly dangerous to the uniformed officer, that means there is cause that the suspect is likely to commit the serious crime of assaulting a uniformed police officer. Further, a lot of the scenarios that are easy to think up involve facts where it is very hard to believe there would be articulable facts the suspect is armed and dangerous: An officer can't just walk up to someone and part them down because the person won't have specific and articulable facts to believe they are armed and dangerous. So I think this problem is of more theoretical interest than practical import, and is arguably not even raised by the facts of the Johnson case.

  In my view, Arizona v. Johnson should be a very easy and narrow decision. Johnson was still seized throughout the stop because he was never given a sign that he could leave under Brendlin v. California. The officer's testimony that she thought Johnson was free to leave is irrelevant under Devenpeck and Whren (and even if it were relevant, it strikes me as pretty bogus). Also, while the Az. Court of Appeals thought the officer's intent was relevant, its conclusion was a matter of law, not a question of fact, and is therefore entitled to no deference. Given that, Johnson was seized, and the frisk was okay given the articulable facts of dangerousness. The broader conceptual questions are interesting, but not likely to arise very often and best left for another day.