Zealotry of old, mostly negligent, male accepting Trump's overture (9)
I believe the answer is:
extremism
'zealotry' is the definition.
(thesaurus)
'old mostly negligent male accepting trump's overture' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'mostly negligent' becomes 'remis' (I can't justify this - if you can you should give a lot more credence to this answer).
'male' becomes 'm' (common abbreviation).
'accepting' is an insertion indicator (inserted letters are accepted).
'overture' suggests taking the first letters (I've seen 'overtures' mean this).
The first letter of 'trumps' is 't'.
'ex'+'remis'+'m'='exremism'
'exremism' placed around 't' is 'EXTREMISM'.
'of' is the link.
Can you help me to learn more?
(Other definitions for extremism that I've seen before include "The holding of way-out ideas" , "Ultra-radical views" , "Radical party's policy" , "Immoderate view" , "Radical political belief" .)