What is the ruling concerning a Muslim ruler who does not govern by Islamic Sharia, and is he permitted to do so based on the jurisprudence of gradualism (fiqh al-tadarruj)?

Ruling by what Allah has revealed is an imperative obligation and a requisite of faith. Ruling by other than what Allah has revealed oscillates between minor and major disbelief, depending on theler's condition. Gradual implementation of Sharia is permissible if the intention is to consider capacity and inability; for Allah does not burden a soul beyond its scope. Whatever Sharia rulings can be implemented without a predominant corruption must be implemented.