Comment: where in the US Constitution it says

that they can detain people/tourists based on them not being able to answer in which stores they will do their shopping?

matter of fact people like John Gunby Casimir Pulaski and many others came to US from Europe to fight for your freedom.

They brought guns and at the border/point of entry nobody asked them which stores they will do their shopping.

as I write these words tens of thousands YES tens of thousands of people are in immigration detention centres placed all across US often within airports.
They are held there for weeks often months - I read heart breaking letters of business people arriving at the LA airport from Brazil and being detained.