Clinton perhaps fears following old amendments to US Constitution (4,2,6)
I believe the answer is:
bill of rights
'amendments to us constitution' is the definition.
(part of the US constitution)
'clinton perhaps fears following old' is the wordplay.
'clinton perhaps' becomes 'Bill' (US president Bill Clinton).
'fears' becomes 'frights' ('fright' can be a synonym of 'fear').
'following' says to put letters next to each other.
'old' becomes 'o' (abbreviation).
'frights' put after 'o' is 'ofrights'.
'bill'+'ofrights'='BILL OF RIGHTS'
(Other definitions for bill of rights that I've seen before include "US constitutional amendments guaranteeing individual freedom" , "1689 English constitutional settlement" , "Statement of people's entitlements" , "law" .)