IANAL, but in many places the Constitution specifically calls out citizens vs non-citizens and in other places does not make an explicit distinction. The bill of rights is one place it doesn't explicitly specify, and indeed uses language that elsewhere was used to indicate it applying to citizens and non-citizens. Of course that interpretation fell away during the cold war and is less popular now.
The "Patriot Act" (which was supposed to be temporary) has permanently eroded those rights.
By what statute do they maintain those authorities if the authorizing legislation has expired?
> The reauthorizing legislation makes permanent 14 of the 16 sunsetted USA PATRIOT Act provisions and places four-year sunsets on the other two
> and places four-year sunsets on the other two
It looks like those were sections 206 and 215, which were somewhat weakened by the same act.
Confusingly, there's a third provision, the "lone wolf" provision, which was extended during the Obama administration; that seems to be part of the Intelligence Reform and Terrorism Prevention Act of 2004 and got rolled into the "USA Freedom Act" reauthorization in 2015.