Thus the head of state gets the message (3)
I believe the answer is:
sos
'the message' is the definition.
'thus the head of state' is the wordplay.
'thus' becomes 'so' ('so' can be a synonym of 'thus').
'the head of' says to take the initial letters.
The initial letter of 'state' is 's'.
'so'+'s'='SOS'
'gets' is the link.
(Other definitions for sos that I've seen before include "Appeal for help" , "Call for help" , "request for aid" , "Morse Code for help" , "Help code in 13 Across" .)