Millions are putting in short order for arrangement of treatment (8)
I believe the answer is:
medicare
'arrangement of treatment' is the definition.
(US health insurance programme)
'millions are putting in short order' is the wordplay.
'millions' becomes 'mare' (I am not sure about this - if you are sure you should believe this answer much more).
'are putting in' is an insertion indicator.
'short' means to remove the last letter.
'order' becomes 'edict' (synonyms).
'edict' with its final letter taken away is 'edic'.
'mare' enclosing 'edic' is 'MEDICARE'.
'for' is the link.
(Other definitions for medicare that I've seen before include "US health scheme" , "US health insurance programme" .)