I don't think he actually has any really significant core support, at least, certainly not in the pejorative way his critics imply. In fact, the opposite is more likely true; he enjoys fairly broad appeal.
In politics, "base" is a term used to suggest your opponent's support is fully made up of lunatic extremist true believers and is utterly devoid of any wider, mainstream appeal.
"Plenty of strikers can score goals," he said, gesturing to the famous old stands casting shadows around us.
"But a lot have found it difficult wearing the number 9 shirt for The Arsenal."