Who better to surveil than those who may have access to state secrets, and are actively talking with representatives of other countries? Members of Congress should be at the top of the list for NSA surveillance.
Perhaps more important to note: are, and its not a secret.
Members of government in general have very little expectation of privacy when it comes to their communications, to the point that it's a significant issue with Hillary Clinton's private email server that the mail is unrecoverable in some cases for auditing purposes.
The rights and obligations of a member of congress and the rights and obligations of a cabinet secretary appointed at the pleasure of the President are fundamentally different. They are not just 'members of government'.
Members of government in general have very little expectation of privacy when it comes to their communications, to the point that it's a significant issue with Hillary Clinton's private email server that the mail is unrecoverable in some cases for auditing purposes.