I never understood the association atheism had with marxism.

Marxism is the materialist interpretation of history, and there is no actual material evidence of God. There is no reason to believe in God if you have no evidence that God exists and is actually the way religion posits it.

Ask any leftist today if they believe in some higher power they are bound to say yes

Do you have any statistics to back that up or are you just going to ignore the entire history of state atheism in past and present socialist countries?