One can't explain America's national leaders being so pacific! (5)
I believe the answer is:
ocean
'so pacific' is the definition.
'ocean' can be an answer for 'pacific' (I've seen this before). I am unsure of the 'so' bit.
'one can't explain america's national leaders' is the wordplay.
'leaders' suggests taking the first letters.
The initial letters of 'one cant explain americas national' is 'OCEAN'.
'being' acts as a link.
Can you help me to learn more?
(Other definitions for ocean that I've seen before include "Large expanse of water" , "Indian or Arctic, say" , "The deep" , "A mighty sea" , "tons of water" .)