The US absolutely does grant full constitutional rights to noncitizens who are physically inside the US, excepting only those inherently tied to US citizenship. (Those are surprisingly few - there is actually not even an explicit right to vote stated in the US constitution, but certainly it is constitutional that noncitizens are not generally allowed to vote).
At border checkpoints on US soil, the border search exception to the Fourth Amendment which this court is interpreting narrowly does not differ based on citizenship. I think there is even no difference about the Fifth Amendment protection against self-incrimination in that context.
Of course, noncitizens do not have the same constitutional right to enter the US as do citizens, which is the same rule that most countries use. So refusing to cooperate at the border could block a foreigner from entering the US in ways it can’t for a citizen.
It is unfortunately also true that US constitutional rights only apply to noncitizens who are physically outside the US in very particular situations and not most of the time. (US preclearance border checkpoints on foreign soil count as physically outside the US for this purpose.) By contrast, US citizens at least in theory fully retain those protections with respect to US government actions wherever they are in the world when the US government ought to know they’re dealing with a US citizen.
That sounds too good to be true. I neither have the legal skills nor the knowledge about the US constitution to tell you where it's incorrect.
I occasionally read the AMA of the immigration lawyer here on HN just for curiosity. I have no intention whatsoever to work in the US, but my impression is that many aspects of visa system sound like treating foreigners as shit in real life. Weird rules, lack of resources, in practice if things go wrong for reasons unrelated to the person you'll lose your visa. Does not sound like full rights when on American soil.
There are indeed many things about the US system that treat foreigners as shit with respect to visa access. But none of that is about giving fewer constitutional rights to foreigners who are physically inside the US.
Visas only control the permission to travel to the US and to apply for admission at a port of entry, and all visa applications and decisions happen while the people taking the action are outside the US. (Visas are only formally applied for at the visa interview, which is never conducted in the US, and visa denials are also issued by the relevant US embassy or consulate abroad and not by the Washington-based part of the State Department.)
The continued legality of anyone’s status within the US following a legal entry does not depend on their visa remaining valid or unexpired. Even if their visa is revoked while they are in the US, that itself only affects future entries, although other actions might of course be taken by the government in parallel.
Importantly, the right to be allowed to enter or remain in the US is one of the constitutional rights that only exists for citizens, no different from most countries. I did say that those few rights which are inherent to citizenship don’t apply to foreigners inside the US. Again, I know of no country in the world which gives foreigners a right to enter and remain, except for conditional rights for specific nationalities like with EU freedom of movement.
Here are two examples of how foreigners have more (and approximately full) rights while inside the US:
Foreigners in the US have far more due process rights if the federal government starts a factually or legally unjustified removal proceeding against them than if a visa officer abroad makes factual or legal errors when denying a visa. The former scenario can often be challenged in administrative, quasi-judicial, or actual judicial proceedings; the latter case has no remedy except to persuade the State Department to change its mind.
If the US government sniffs the communications of two foreigners located within the US, they need a warrant under the same conditions as they would if the foreigners were citizens, unlike the case of purely external communications where the US government is only so constrained if they know a citizen is involved.
At border checkpoints on US soil, the border search exception to the Fourth Amendment which this court is interpreting narrowly does not differ based on citizenship. I think there is even no difference about the Fifth Amendment protection against self-incrimination in that context.
Of course, noncitizens do not have the same constitutional right to enter the US as do citizens, which is the same rule that most countries use. So refusing to cooperate at the border could block a foreigner from entering the US in ways it can’t for a citizen.
It is unfortunately also true that US constitutional rights only apply to noncitizens who are physically outside the US in very particular situations and not most of the time. (US preclearance border checkpoints on foreign soil count as physically outside the US for this purpose.) By contrast, US citizens at least in theory fully retain those protections with respect to US government actions wherever they are in the world when the US government ought to know they’re dealing with a US citizen.