Here’s a “fact check.” Four American presidents have been .
Besides Unitarians, a lot of the founders and early Presidents (the Southerners) were formally Episcopalians, which didn’t necessarily mean more than that they were born into an Episcopalian family. The “born again” churches demand an adult personal commitment at some point for someone to become a real member, whereas Episcopals (and Catholics and Lutherans, and probably Orthodox, and maybe Van Buren’s Dutch Reformed) just default people in at birth. This whole infant v. adult baptism controversy really does have some substance to it; it’s not one of those controversies based on an obscure textual quibble.
Besides Episcopal, Unitarian, and Dutch Reformed (Van Buren), most of the early Presidents seem to have vacillated between Methodist, Presbyterian, and sometimes Baptist or Episcopal, or to have declared themselves to be nondenominational Christians. There might have been good political reasons for this vagueness. Many were not communicant members of any church, and Grant was unbaptized — Polk was baptized only on his deathbed.
To the extent that the first 20 Presidents or so were Christians at all, most of them seemed to be exactly the kind of lax conventional / liberal / nondenominational / non-born-again Christians whose Christianity contemporary fundamentalists and evangelicals tend to doubt. Later on Presidents tended to have more denominational identification and McKinley, Wilson, and others seemed to be devout and committed. But there were still plenty of very nominal Christians, like Eisenhower.