Even if a Mormon social teaching happens to concur with orthodox Christianity at this point in time, it is unreliable and subject to alteration. It's tempting to say that "continuing revelation" has defined Romney's career, who has changed his positions on same-sex marriage and abortion and just about every major "culture war" issue.

For evangelical Christians, Romney has some additional explaining to do. On such essential doctrines as the Trinity and the role of Jesus in salvation, there are major differences between orthodox (biblical) Christianity and Mormonism. But the real problem is that Mormons believe and teach an American history that is in many particulars completely unsubstantiated and in others demonstrably false. Mormons believe that the "lost tribes" of Israel actually ended up in America, and that Jesus visited America and these tribes during his incarnation. These are just a few of Mormonism's highly idiosyncratic views of history.

Does Mitt Romney believe these views? Why or why not? Does he believe historical facts are matters of personal opinion? More to the point, does he really believe that, if he were to become the GOP nominee, he would not have to answer these questions before the world? Romney will face a Hobson's choice. He will either affirm certain beliefs about reality and American history that most Americans will find false or flimsy, or else he will reject them be thereby "outed" as a hypocrite or traitor to his own belief system.

The vast majority of Americans won't care about these theological implications. Indeed, Americans are generally tone-deaf to theological nuances. But to all American voters—religious or not—I would ask this question: Do we want a person who believes that history is something you can "make up as you go along" negotiating the outcomes of conflicts with real histories that go back thousands of years? Conflicts in the Middle East, in Asia, and elsewhere require an understanding of history and human nature that are not fabricated out of whole cloth.

Again, I do not want to diagnose Mormonism book, chapter, and verse. But let me be plain on this point. At its core, Mormonism is—by Christian standards or by reasonable secular standards—an a-historical (and at times anti-historical) worldview. Evangelicals and others who argue that you cannot dismiss Romney based on his religion either miss or ignore this critical point. The boat of Mormonism is not tied to the anchor of either historical Christianity or even commonly accepted historical facts. Because the boat of Mormonism has been cut loose from that anchor, and is adrift in a sea of philosophies and ideas, any similarity between Christian and Mormon is historically temporary and not a reliable gauge of how Romney will govern.

Let Me Tell You about Our President

My final point may seem minor to most Americans, but I think it should make a significant difference to evangelicals: As Theodore Roosevelt said, the presidency is a "bully pulpit." Indeed, it has become the bulliest pulpit in the world. The entire planet hangs on what the occupant of that pulpit says and does.

Placing a Mormon in that pulpit would be a source of pride and a shot of adrenaline for the LDS church. It would serve to normalize the false teachings of Mormonism the world over. It would also provide an opening to Mormon missionaries around the world, who could start every conversation: "Let me tell you about the American president." To elect a Mormon President is to advance the cause of the Mormon Church.