Rick Santorum’s near-miss in Iowa provides a reminder that, for many Republican voters (and not a few candidates), religion and politics overlap. If you need another reminder, though, consider this: recently, the Smithsonian has restored and put on display a weird and fantastic 19th-century book known as “The Jefferson Bible.” That’s Jefferson as in Thomas, and this private, personal document offers a useful case study in how politics and Christianity have mixed it up in American history, right up to today.

To understand Jefferson’s Bible, you need to start with the one book he published in his lifetime: “Notes on the State of Virginia.” Jefferson wrote this survey in the 1780s, organizing it around topics like “The different religions received into that State.” But the book came back to haunt him two decades later when he was battling John Adams for the presidency. Indeed, long before Rick Perry’s and Mitt Romney’s books caused them trouble on the campaign trail, Jefferson had to deal with some very specific attacks on what he’d written about religion.

Those attacks became a key issue in the election of 1800. While Jefferson referred to “Nature’s God” in the Declaration of Independence, he preferred to keep his personal beliefs to himself, a reticence that lined up with his philosophy of individual freedom and religious tolerance. In “Notes,” he put it this way: “It does me no injury for my neighbor to say there are twenty gods, or no god. It neither picks my pocket nor breaks my leg.”

In a presidential campaign, and in the hands of Jefferson’s enemies, this passage became proof of the candidate’s radicalism. One popular pamphlet from a pro-Adams minister quoted “Notes,” then countered it: “Let my neighbor once persuade himself that there is no God,” the minister warned, “and he will soon pick my pocket, and break not only my leg but my neck.”

Such attacks proved effective enough that, when Jefferson did win the election, some families buried their Bibles in their gardens, fearing the new president would burn them. So it made sense that Jefferson continued to keep his religious views private. Years later, after he and Adams had resumed a correspondence, Jefferson described Jesus’ teachings as “the most sublime and benevolent code of morals.” The problem, he wrote in another letter to Adams, came in the “artificial scaffolding” that surrounded those teachings — the Virgin Birth, the miracles and so on.

“The Jefferson Bible” is his attempt to tear down that scaffolding. Jefferson took his first stab at it while still president. In the White House, “after getting through the evening task of reading the letters and papers of the day,” he used a razor to slice Jesus’ teachings out of a couple of King James Bibles, then grouped them by subject (e.g., “false teachers”) and pasted them into a scrapbook. Its title page included these words: “an abridgment ... for the use of the Indians.” Scholars agree it was most likely a sly joke about the impossibility of circulating such a genuinely radical book, or perhaps a joke about Adams’ political allies, whom Jefferson referred to as “Indians” in his second inaugural.

That scrapbook didn’t survive, other than a copy of its title page. What did survive is a second, more elaborate version Jefferson created once he retired. This one includes four columns of text (Greek, Latin, English, French) from the Gospels, and Jefferson had his bookbinder cover it in gold-tooled red leather. Jefferson preserved Jesus’ life story and his teachings, but he removed anything that strained reason — the walking on water or Lazarus’ resurrection. And Jefferson applied this standard to the smallest details. Matthew 19:2, for example, reads: “And great multitudes followed him, and he healed them there.” But Jefferson carefully excised “and he healed them there.” The Smithsonian has published a gorgeous full-color facsimile of the restored Bible, and it shows the comma after “him” just dangling there.

“The Jefferson Bible” ends with Jesus’ entombment, and, given all the trouble caused by his published thoughts on religion, Jefferson seemed happy to take the book to his grave. When he mentioned it in letters to a small circle of friends, he cautioned them to keep it a secret. Even his family didn’t find out about it until after he’d died.

In 1895, his heirs sold the book to the Smithsonian for $400. A few years later, a congressman — a devout Christian from Iowa, as it happens — wrote a widely reprinted article about it. The government produced an extravagant edition at a cost to taxpayers of more than $500,000 in today’s dollars. Some protested the price. Others argued about whether the book confirmed or refuted Jefferson’s atheism. Still, in 1904 the government published more than 9,000 copies, with 14 going to each congressman — and with enough kept in reserve that a copy also went to every incoming representative or senator, a tradition that continued through the 1950s.

Today, the facts about “The Jefferson Bible” might seem like an impossible obstacle to anyone who wants to fashion Jefferson as a hero for right-leaning Christians — and America as a “Christian nation.” Instead, the book has been distorted to fit the religious right’s agenda.

There’s no better example of this than David Barton, an amateur historian who’s become quite popular with Perry, Santorum and Michele Bachmann. Barton loves archival flourishes — his Texas offices include a concrete vault filled with 18th century arcana — but his true concerns lie in the present. Though Barton admits that “The Jefferson Bible” often comes up as proof that its namesake wasn’t the evangelical Christian conservatives want him to be, he also says he can refute this. In a TV appearance in 2010, Barton fixated on Jefferson’s “Indians” title page, mixed in some unrelated material about Jefferson’s Indian policy, then pivoted to an outrageous fabrication: “He then gave it to a missionary,” Barton said of Jefferson and his Bible, “and he said, ‘Here, if you get this printed, and you use this as you evangelize the Indians.’”

There’s absolutely no evidence of Jefferson giving either version of his Bible to anyone other than his bookbinder. Perhaps it’s no surprise that last year, in Iowa, Newt Gingrich said, “I never listen to David Barton without learning a whole lot of new things.” That’s because Barton loves to cherry-pick a phrase and manipulate it support his side in a partisan, present-day debate.

But there’s a bigger problem with Barton’s method: He strips history of its complex human appeal. After all, “The Jefferson Bible” stands as one of the most interesting and iconoclastic moments in America’s religious past — one man with a razor, a pot of paste and a unique and private set of ideas. They were intricate ideas: Jefferson was no more a Bible thumper than he was a Bible burner. And that’s why he and his handmade book have enjoyed such an odd and exciting afterlife. After one politician got his 14 copies of the 1904 edition, he reported receiving more than 2,000 requests from his constituents.

Let’s hope just as many people seek out the new Smithsonian edition, where they can see for themselves what Jefferson spent so much time making — and no doubt reading as well.

• Fehrman is working on a book about presidents and their books. He wrote this for the Los Angeles Times.