Earlier today, the Supreme Court held oral argument in Navarette v. California, a Fourth Amendment case on when the police can lawfully pull over a car based on an anonymous tip of wrongdoing. I want to offer a few thoughts on the argument, and in particular to try to explain one potential source of confusion.  Unfortunately, the Court has not yet posted the oral argument transcript. All I have to go on right now are others’ reports.  So I’ll offer this post for now, assuming those reports are accurate, and if necessary I’ll follow up after the transcript is available.

The facts of the case are very simple.  A 911 caller reported that he had just been run off the road while going southbound on Highway 1 near a specific mile marker by a silver Ford F150 truck with California license plate number 8-David-94925.  Officers spotted the truck and pulled it over.  The question in the case is whether the officers had lawful authority to pull over the truck based on the tip.

Longstanding Supreme Court precedent says that the police can make an investigative stop of someone if the police have reasonable suspicion, based on specific and articulable facts, that a person is engaged in or is wanted in connection with criminal activity.  The question is, did this tip meet that standard, such that the police could pull over the car when they spotted the truck?

I tend to think that the answer should be that yes, it did: This specific tip was sufficient.  To my mind, the key is that the tip did not just make a general claim that the driver of a Ford F150 truck was drunk.  That weak level of detail would have made the tip analogous to Florida v. J.L., where an anonymous tip that a suspect was carrying a gun was held insufficient.  Instead, the tip here made a specific allegation of wrongdoing.  The caller alleged that the driver of the truck ran him off the road.  The tip also provided detail about the model of the car and even the license plate number, together with information about where the truck was located.

As I see it, when the police found the truck, with a license plate number matching the tip, driving in the rough location that the tip predicted it would be, that verification provided enough corroboration of the tip that the police had reasonable suspicion to pull over the truck and investigate.  Of course, it’s possible that the tip was false.  Someone might have been upset at the driver of the truck for some other reason, and might have made a bogus report just to inconvenience them.  But while it’s possible, it doesn’t seem all that likely.  At the very least, it doesn’t seem like enough of a possibility to keep the specific tip from amounting to reasonable suspicion.

If oral argument reports are accurate, though, much of the argument focused on hypotheticals involving immediate dangers.  Here’s SCOTUSblog’s Lyle Denniston:

[The lawyer for the defendant was] led into a concession that maybe the Court would want to find a way to create an exception if the tipster had said that someone was driving into Los Angeles with an atomic bomb with the intent to explode it, or had said that he had seen a kidnapping in which a child was put into the trunk of a car that then drove off.

But even that concession was not acceptable to some; Justice Antonin Scalia said that, if [counsel for the defendant] were willing to make those exceptions, then the constitutional question was nothing but an argument about details, so where was the dividing line under the Fourth Amendment?

Let me offer an answer to Justice Scalia’s question: The dividing line is the line between the doctrine of Terry v. Ohio and the doctrine of exigent circumstances. In Terry and later cases interpreting it, the Supreme Court created specific rules for when the police can make stops to investigate reports of criminal activity. The reasonable suspicion standard is the line the Court drew; it requires a particular threshold of information about a crime to justify a stop.

Exigent circumstances is a different branch of Fourth Amendment doctrine that applies to a different set of problems. The exigent circumstances doctrine recognizes that the police sometimes need to act quickly to prevent a future harm. Here’s how the Supreme Court expressed the doctrine in a recent decision, Missouri v. McNeely (with internal quotations and citations omitted):

A variety of circumstances may give rise to an exigency sufficient to justify a warrantless search, including law enforcement’s need to provide emergency assistance to an occupant of a home, engage in “hot pursuit” of a fleeing suspect, or enter a burning building to put out a fire and investigate its cause. As is relevant here, we have also recognized that in some circumstances law enforcement officers may conduct a search without a warrant to prevent the imminent destruction of evidence. While these contexts do not necessarily involve equivalent dangers, in each a warrantless search is potentially reasonable because there is compelling need for official action and no time to secure a warrant.

To determine whether a law enforcement officer faced an emergency that justified acting without a warrant, this Court looks to the totality of circumstances. We apply this finely tuned approach to Fourth Amendment reasonableness in this context be-cause the police action at issue lacks the traditional justification that a warrant provides. Absent that established justification, the fact-specific nature of the reasonableness inquiry, demands that we evaluate each case of alleged exigency based on its own facts and circumstances.

In my view, the hypotheticals that were tossed around at oral argument were about exigent circumstances, not Terry stops. The reason that the police should be able to pull over a car based on an uncorroborated tip about a nuclear bomb or rescuing a kidnapped kid is that the police need to act immediately to stop the harm. The point of such a stop is to save lives, not to try to gather evidence about a criminal case.

The precise line between Terry and exigent circumstances can be tricky, I realize. We criminalize conduct that we think is very harmful. As a result, reports of something really harmful afoot are also likely to be reports of criminal activity. But it’s important to keep the two lines of cases distinct. That distinction explains why uncorroborated anonymous tips generally won’t justify stops but such tips about immediate dangers can. And it also explains why the Justices don’t need to and shouldn’t introduce a vague factor of the seriousness of the offense into the Terry framework. That “factor” already matters under the exigent circumstances doctrine, and it is not based on a generalized notion of seriousness but rather the threat posed based on the specific facts and circumstances.

The Justices don’t have to get into these issues to resolve Navarette. For the reason I explain above, I think the tip in this case was enough to generate reasonable suspicion under Terry. But if they do want to deal with stops based on immediate dangers, I think the path forward is the doctrine of exigent circumstances, not the doctrine of Terry v. Ohio.