Per the Debian Reference I added the following to /etc/pam.d/su:

# anti-RMS configuration in /etc/pam.d/su
auth required pam_wheel.so group=adm

# Wheel members to be able to su without a password
auth sufficient pam_wheel.so trust group=adm


This was working for many months. I have the admin account and another account that were able to su without having to enter the password. Now
it's back to prompting for the password but the two accounts I use are still in the 'adm' group so I don't understand what is causing this behavior. The pam_wheel.so module is the same one that was in use when things worked.

Any thoughts what could be causing the problem will be received gratefully and with a 'virtual hardy handclasp'.