There is No Such Thing as "Theism," "Christian Theism" or "Mere Christianity"
First, there are many varieties of theism. Islam is a theism, as is Judaism. Polytheism is a theism. So is pantheism and panentheism. Deism is one too, at least earlier versions of it.
Wikipedia's entry for "Theism" says this:
In a more specific sense, theism is commonly a monotheistic doctrine concerning the nature of a deity, and that deity's relationship to the universe. Theism, in this specific sense, conceives of God as personal, present and active in the governance and organization of the world and the universe. As such theism describes the classical conception of God that is found in Christianity, Judaism, Islam, Sikhism and Hinduism.I've said this before and I'll say it again, there is no such thing as a generic theism. Yes, the term "theism" can indeed be used to represent these arbitrarily selected theistic doctrinal beliefs. However, theists believe more than this. We will never find a theist who only believes these things. That's where the agreement ends. So there is no such thing as a theist. There are only Muslims, Jews, Christians, Sikhs and Hindus.
Second, there are many varieties of Christian theism, as we know all too well, which includes existential Christian theism, mystical Christian theism, Process theism, and Open theism (the evangelical sect from Process theism). Historically there have been many varieties of Christian theism like the various "heretical" ones that were condemned and killed off, some of which can be seen in Bart Ehrman's book, Lost Christianities: The Battles for Scripture and the Faiths We Never Knew.
Third, just as there isn't such a thing as theism or Christian theism, there isn't anything such as "mere Christianity" either. -- See link.
So I don't usually talk in terms of "theism" or "Christian theism." To do so is like saying I know what theism or Christian theism entails. I don't. In America where evangelicalism seems to make the loudest noise doing so would be taking a stand with the evangelicals, that they represent Christian theism. This is something I object to. By saying we know what Christian theism entails is like saying we prefer one cigar over another when we don't smoke. ;-) I usually talk about religions, specific ones, not theism, Christian theism, or mere Christianity, since they do not exist. I adjure others to do the same.