[John Beresford Tipton]

The legal issue boils down not to the patron's rights, but because the records are the records of the library, it is the right of that institution that are in question.

The fourth amendment protects the library from having to fork over its records without a warrant, issued on probable cause.

[Tunehead54]

The right of the people to be secure in their persons, houses, papers and effects, against unreasonable searches and siezures shall not be violated ...

I think one can argue that your library records, as say your banking records, are "effects" within the meaning of the 4th Amendment and thus not just a "library" issue but that of the patrons as well.