Careful about the "warrantless" here. It's true, it's a warrantless search, and don't think I'm saying that's an illegitimate concern. However:
The police already have broad authority to search you and your immediate person incident to an arrest. If this is news to you, you really want to read up on it. This is one of the big things that makes a formal arrest different from mere detention, and one of the reasons the ACLU guides and things like that instruct you to clearly ask if you're "under arrest".
All the DoJ is saying here is that a cellphone is, like your pockets and your bags, a legitimate target of a search incident to arrest. There's apparently a circuit split on the issue. There are other things that aren't legit incident to arrest; for instance, certain kinds of car searches aren't lawful solely because of arrest (trunks can be searched if cars are impounded, but only for "inventory", and can't be searched IIRC if the car isn't impounded; similarly, being arrested outside won't give the police the automatic authority to search your house).
The search incident to lawful arrest doctrine is rooted in officer safety. Specifically, the Court says officers should have the ability to look for guns and contraband when someone is pulled over and it's likely they are armed or their immediate person or vicinity poses a threat and/or has evidence of a crime. The courts have decided that any drug suspicion means they are likely to have a weapon, which is unfortunate, but at least based in some reality.
To my knowledge, the only court (and courts are split) that has allowed electronics to be searched is when a drug dealer was pulled over in California and incident to lawful arrest, the officer downloaded the call history to help them find others involved in the drug trade.
There is NO COURT to my knowledge that would authorize warrantless search or confiscation of someone's cell data, computer data, jump drives, etc. without an arrest taking place. That is a fishing expedition and it's exactly what the Court has ruled unconstitutional under the 4th amendment.
This is where I get very frustrated with the NSAs ability to collect the call information in the first place. The only reason to collect it is to fish later—that's not how the law is supposed to work.
These are complex problems that very few judges or lawmakers have enough understanding of technologically to make informed judgement, IMHO, however.
EDIT - My best guess is that the Court will allow basic access to a cell phone taken in a lawful arrest. I.E., like the article linked above, an officer would be able to look at the call history, but not necessarily download the content of the phone. I think the offender's brief will likely ARGUE that the phone not be accessed at all, with the true hope being the Court merely limits what officers can do.
I have a hard time believing they won't let officers look at any of the electronics with them. I also hope they don't just let officers download everything carte blanche.
The case we're talking about was search after arrest.
If immunity [to a warrantless search] is to be conceived of as a rule, there is one exception that has been established as firmly as the rule itself. The government may search the person of the accused when legally arrested to discover and seize the fruit or evidences of crime.
also (cited in Harris v US):
The right without a search warrant contemporaneously to search persons lawfully arrested while committing crime and to search the place where the arrest is made in order to find and seize things connected with the crime as its fruits or as the means by which it was committed, as well as weapons and other things of effect an escape from custody is not to be doubted.
Officer safety is one of three motivations for search incident to arrest I've read about; two more are evidence collection (as above), and mitigating the risk that evidence that could later be collected via warrant might be destroyed.
Terry stops, on the other hand, are motivated solely by officer safety.
I said rooted in officer safety, not solely because, ;-).
Even if the search happens AFTER the arrest (assuming it's lawful, without that there is no internal link to a legal search), the court is still going to look at whether the seized item was taken incident to the arrest. That's why trunk's can't be searched unless there is a "particularized" reason, i.e. drugs, contraband, other evidence of the specific crime for which the offender was arrested for.
Under that line of reasoning, it's pretty likely courts would be ok with thumbing through the offender's call history to find other possible offenders for the related crime.
Not saying it's right, but that's how the law is evolving on evidence collection. Truth is, we need much deeper analysis on the technology at hand, but our courts are OLDDDDDDDD. Not saying octogenarians can't make effective re: technology, but it certainly hasn't bore out that way yet.
You note that a "drug dealer" faces a warrantless search of his electronic devices to determine others involved in the "drug trade" but how is the determination that a suspect is a "drug dealer" made?
Is this another discretionary power afforded to LEO?
Drugs laws, and the Court's interpretation of handling drug crimes gives officers a lot of latitude. I forget the name of the Court case that allows officers to intuit that ANY drug-related offender can be presumed to have a weapon, but the data was actually fairly compelling (without knowing how the data was derived, the outcome was pretty clear—statistical significance that people with drugs are likely to have weapons.
There's also a lot of law about "the person was a SUSPECTED drug offender" because they drove erratically, or were in the wrong neighborhood, or threw something out of the car..... basically anything, and those people can be treated much like folks found to have drugs on them in the first place.
But, if there is no reason to truly arrest someone, the search / seizure shouldn't take place. You usually don't get arrested for minor ordinances... (tickets, lane violations, etc.)
My example was more or less just a common example.
To my mind, if someone was arrested for selling pirated software on jump-drives, the officer would likely be able to check out the call log to look for other conspirators.
The police already have broad authority to search you and your immediate person incident to an arrest. If this is news to you, you really want to read up on it. This is one of the big things that makes a formal arrest different from mere detention, and one of the reasons the ACLU guides and things like that instruct you to clearly ask if you're "under arrest".
All the DoJ is saying here is that a cellphone is, like your pockets and your bags, a legitimate target of a search incident to arrest. There's apparently a circuit split on the issue. There are other things that aren't legit incident to arrest; for instance, certain kinds of car searches aren't lawful solely because of arrest (trunks can be searched if cars are impounded, but only for "inventory", and can't be searched IIRC if the car isn't impounded; similarly, being arrested outside won't give the police the automatic authority to search your house).