Third party doctrine cuts deep. See Couch v. US, 409 U.S. 322, 335 ("there can be little expectation of privacy where records are handed to an accountant..."). For example, all the prosecuting of banks and big corps that the Daily Show cheers on depends quite heavily on investigators having access to third-party accounting and financial records. The doctrine might need to be reformed, but it's a monumental task touching many areas and longstanding practices.