First, it engages in question-begging---assuming what one wants to prove. It begins with the assumption that God exists, and then concludes that God exists. Such reasoning would get you an "F" in any logic class worthy of the name!
i) In a stock Van Tilian dialogue, the apologist asks the unbeliever to assume the truth of Christianity for the sake of argument, then consider the explanatory power of Christianity. Presupposing Christianity is a thought-experiment. And a hypothetical scenario isn’t begging the question.
ii) Conversely, the apologist assumes the truth of atheism (or some other non-Christian worldview) for the sake of argument, then asks the unbeliever a series of Socratic questions to show how his non-Christian worldview lacks explanatory power.