Nato abandoning borders one time with difficulty (2,1,7)
I believe the answer is:
at a stretch
'with difficulty' is the definition.
(I've seen this before)
'nato abandoning borders one time' is the wordplay.
'abandoning borders' says to take the centre (the borders of the word are removed).
'one' becomes 'a' (a thing is one thing).
'time' becomes 'stretch' (I've seen this before).
The middle of 'nato' is 'at'.
'at'+'a'+'stretch'='AT A STRETCH'
(Other definitions for at a stretch that I've seen before include "With difficulty; without interruption" , "Running, possibly" , "in one continuous period" , "With much effort" .)