Cajolery frequently succeeded in ongoing saga (4,4)
I believe the answer is:
Here is my best explanation:
'cajolery' is the definition.
(soft soap is a kind of cajolery)
'frequently succeeded in ongoing saga' is the wordplay.
'frequently' becomes 'oft' (I've seen this before).
'succeeded' becomes 's' (genealogical abbreviation).
'in' is an insertion indicator.
'ongoing saga' becomes 'soap' (TV soap opera).
'ofts' going inside 'soap' is 'softsoap'.
(Other definitions for soft soap that I've seen before include "Persuasive flattery", "Use persuasive flattery", "butter", "Flattering talk from tender cleanser?", "Flattery - blarney", "Blarney", "Make flattering comments", "persuasive talk", "Flattery of cleansing sort?" and "(Use) flattering talk".)