Millions up, USA lost for being faint-hearted (13)
I believe the answer is:
pusillanimous
'being faint-hearted' is the definition.
(I've seen this before)
'millions up usa lost' is the wordplay.
'lost' indicates an anagram.
'millions'+'up'+'usa'='millionsupusa'
'millionsupusa' is an anagram of 'PUSILLANIMOUS'.
'for' is the link.
(Other definitions for pusillanimous that I've seen before include "Fearful" , "Weak" , "Craven" , "Weak-spirited - timid" , "Lacking determination" .)