The notion of a creator God leads to an infinite regress because such a being would have to have been created

Any God capable of designing a universe must be a supremely complex and improbable entity who needs an even bigger explanation than the one the existence of such a God is supposed to provide. 

Dawkins also says that the hypothesis that an intelligent designer created the universe is self-defeating... intelligent design hypothesis claims to provide an ultimate explanation for all existing improbable complexity and yet cannot provide an explanation of its own improbable complexity. 

Dawkins further states that the God hypothesis creates a vicious regress rather than terminating one. Similarly, Harris follows Dawkins’ in arguing that the notion of a creator God leads to an infinite regress because such a being would have to have been created

This assumption that God would need an extenal cause flies in the face of the longstanding theological assumption that God is a perfect and so necessary being who is consequently self-existent and ontologically (scientifically) independent.