He's a Muslim. Pure and simple. He even said so, 3 times and ABC news corrected him. Four years ago I would not see myself voting for anybody who was not a Christian. You can add me to that list of voters now (at least for this year).
I'll take an atheist over a Muslim any day. Sure do wish there was the option of voting for a Christian though.
Since agnostic was not on the list as distinct from atheist, it’s not possible to tell from this what kind of support a militantly atheistic candidate would get. But I’d say: Probably not a lot, compared to the agnostic.