so that the whole of a thing or a person is affected :
She was shaken to the core by the news.
He's a politician to the core (= in all his attitudes and actions) .
TO THE CORE
Meaning of TO THE CORE in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005