English writer makes US president (silly cow!) cross (4,5,4)
I believe the answer is:
ford madox ford
'english writer' is the definition.
(novelist Ford Madox Ford)
'us president silly cow cross' is the wordplay.
'us president' becomes 'ford' (Gerald Ford).
'silly' becomes 'mad'.
'cow' becomes 'ox'.
'cross' becomes 'ford' (fording is a kind of crossing).
'ford'+'mad'+'ox'+'ford'='FORD MADOX FORD'
'makes' is the link.
(Other definitions for ford madox ford that I've seen before include "English novelist" , "Writer" .)