At the US international border, no, even US citizens can’t prevent the phone search regardless of whether or not they consent. They can however usually decline to give a PIN, passcode, or password or to assist in unlocking the phone by entering such a credential, and they can’t be refused entry to the US. However, CBP can then temporarily seize the phone to perform a more comprehensive attempt at searching it. Getting the phone back later may be a hassle.
Additionally, pissing off CBP may lead to extended delays, luggage searching, and questioning to see if they can find another legally valid reason to punish you for annoying them. And maybe they might revoke trusted traveler program membership due to no longer seeing you as a low-risk traveler. But indeed, they will not finally refuse entry to a citizen.
There are rarer cases where the US government can insist on your cooperation in getting past a PIN, passcode, or password, such as if you show them that an incriminating document exists on your phone and then lock the phone before they can collect the evidence.
And while the exact boundary of the constitutional protections regarding face or fingerprint unlock is not authoritatively settled nationwide in the courts, it’s very likely weaker than for information you hold in your mind like a password.
I strongly suspect CBP can constitutionally require a US citizen entering at an international port of entry to assist with fingerprint or face unlock, though I admit I don’t know how physically they can force the matter if the person refuses. It wouldn’t surprise me if that would be grounds for arrest under at least some circumstances (maybe not all).
While I was born after 9/11, I'm think I've heard that these unprecedented powers were given to CBP (and other border agencies around the world) after that event.
Most people crossing any border face little friction like this, but when you dig in and see what border agents are allowed to do, it gets a bit unnerving. Especially so for the US, the self-proclaimed land of the free.
Consider this - the CBP is granted wide-reaching powers that can supersede what actual police are allowed to do. They're allowed to racially profile, discriminate, search or detain anyone for any reason - citizen or not. Search warrants aren't required. Punishments like refusing foreigners entry for no reason or marking citizens to be additionally screened for the rest of their life can't be contested and are absolute. They are insulated from being sued, and may not need to follow Freedom of Information requests (not sure if this was reverted or not). They can do any of this within 100 miles of any external US borders - a.k.a. most major cities in the country. You don't actually need to be crossing or have crossed a border to be held up. Freedom!
The more you read into it, the more it seems that the federal US government has written a black check in terms of what some people are allowed to do. In the vast majority of cases, border guards are reasonable and don't overstep any boundaries - but I'm confused at why Americans, with the culture of valuing individual freedoms over all, aren't concerned with the hypothetical consequences these powers provide.
> I'm confused at why Americans, with the culture of valuing individual freedoms over all, aren't concerned with the hypothetical consequences these powers provide.
I don't think this is as much of a "gotcha" it seems to be. People have all kinds of theoretical beliefs that they routinely violate in practice. It's just part of being human.
The way things like this are supposed to work in the real messy human world is that we encode these "freedoms"/rights into a constitution. We then have a judicial branch that protects these rights, irrespective of individual human inconsistency/hypocrisy. For border searches we have the relevant rights in the US constitution already. The problem is that the judicial branch has incorrectly ruled that protections like the 4th amendment don't apply at the border.
Additionally, pissing off CBP may lead to extended delays, luggage searching, and questioning to see if they can find another legally valid reason to punish you for annoying them. And maybe they might revoke trusted traveler program membership due to no longer seeing you as a low-risk traveler. But indeed, they will not finally refuse entry to a citizen.
There are rarer cases where the US government can insist on your cooperation in getting past a PIN, passcode, or password, such as if you show them that an incriminating document exists on your phone and then lock the phone before they can collect the evidence.
And while the exact boundary of the constitutional protections regarding face or fingerprint unlock is not authoritatively settled nationwide in the courts, it’s very likely weaker than for information you hold in your mind like a password.
I strongly suspect CBP can constitutionally require a US citizen entering at an international port of entry to assist with fingerprint or face unlock, though I admit I don’t know how physically they can force the matter if the person refuses. It wouldn’t surprise me if that would be grounds for arrest under at least some circumstances (maybe not all).