Imam Ghazali had strong views on the obligation of the Caliphate. He wrote about the topic in a number of his works, and even penned a defence of the Abbasid Caliph al-Mustazhir Bi-Llah.

Significantly, Imam Ghazali considers the subject so important that he includes it in his writings on creed/beliefs.

This episode is also available as a blog post: http://caliphate1.com/2021/04/02/imam-ghazalis-views-on-the-importance-of-the-caliphate-imamate/