I've been intending to say something about this article in Christianity Today, which has been noted in various places. Some disjointed thoughts:
* It seems to me that the only real way for historical method(s), as such, to prove that X did not happen is to prove that Y, which excludes X, did happen. And to do that, we have to have some notion of what, historically, would have had to be involved in, and as a result of, X's happening (as indeed we must if we want to say that X did, in fact, happen). I haven't read any of Bushman's work, but it seems to me that this is precisely what Bushman is doing. In any case, it seems to me that the proper response to it, if you don't believe it, is not to engage in dismissive rhetoric, but to show that Y happened, or at least, why saying Y happened fits better with the historical evidences.
* If one allows miracles (for instance) to be in general possible, and insists that historical methods exclude them entirely, you must be proportionately insistent that historical method can give you definitely wrong, or at least significantly incomplete, results, even if practiced in an ideal way by an ideal historian on the basis of ideal information. (Much the same, incidentally, with scientific methods.) If you reject miracles in order not to say this, the reasons for that rejection will have to stand philosophically on their own right, independently of that rejection's use in your historical work. (And most arguments against the possibility of miracles in general are extremely poor.)
* But it does not follow from any of this that (say) a Muslim historian's belief in the appearance of the Archangel to the Prophet will have all that much effect on his historical work, even if he does work on the early origins of Islam. For one thing, the appearance is just one event among many events. For another, most of the events that are relevant for getting a grasp of the origins of Islam are communication from man to man, not communication by way of angels. And this should show up more or less the same on the supposition that the first recitation was a delusion or fraud as it would on the supposition that it was a revelation. In other words, once history moves beyond the alleged event itself -- and it has to, if it is to be history -- the question of whether Gabriel really appeared to Muhammad gives way to the effects of people responding to claims of this event as communicated to them.
* Which is not to say, of course, that belief in the truth of such an appearance would have no effect on what the historian sees. Just as a skeptic may see something a believer might miss, so a believer may see something a skeptic might miss. In the Grammar of Assent, Newman subjected Gibbon's 'five causes of the rise of Christianity' to a beautiful believer's critique. What Newman saw that Gibbon did not: Gibbon left out belief in Christ, which was needed to make sense of the five causes, and without which none of the five causes would make any sense at all as historical causes. How could one go about trying to identify the historical causes of Christianity's rise and not take into account at all the sense Christians had (and explicitly said they had) of actually participating in the work of the living, resurrected Jesus? But such is the error a nonbeliever might make, even in doing good history. The idea that a historian can be blinded by belief in X is entirely right; it can also happen, and has also happened, that historians have been blinded by not believing in X. Skepticism about something doesn't magically put you on the right side. Indeed, it doesn't even put you on the right side when you happen to be right. I was reading the other day about Arthur Conan Doyle, and the famous case of the fairy photographs. Obviously, many spiritualists like Conan Doyle defended them, and many skeptics of spiritualism attacked them. If you look at the debate, however, you find that, while the skeptics happened to be right that the photographs were fake, the actual charges they usually brought against them (tampering, etc.) were both unsubstantiated and false. Likewise, one finds that, while Conan Doyle and the like were wrong about the photographs, their defenses of it were top-notch, and, what is more, generally right: the best experts (including Kodak labs) could not identify any tampering, all the evidence pointed against tampering, etc. What both sides were forgetting, of course, is that you don't need to tamper with the film to fake a photograph; they were arguing the subject at the wrong point. But precisely because of that the skeptics were quite as wrong as the believers, and much less rationally justified, since they were actually arguing against the most rational assessment of the evidence on the points they were making. And so it can easily be with history, and probably has been many times. And Kuklick's statement about Bushman, that "his religion is a conversation stopper", sounds to me suspiciously like a case of a skeptic being much less rationally justified in his conclusions than his opponents in theirs.