Ben Carson will take a brief break from the campaign trail to spend a few weeks hawking his upcoming book, "A More Perfect Union." The transition between selling himself as a candidate and selling photos of himself on a bound stack of paper will probably be an easy one. The campaign hiatus doesn't particularly threaten to cause much of a hiccup in his schedule, but it does offer Carson the opportunity to have another pool of money pay for ferrying him around from appearance to appearance.

Candidates love to write books. According to our analysis, 58 candidates for the presidency since the year 2000 have written at least 172 books between them. About a third of those came within two years before a presidential race or within two months afterward.

But very few authors actually go on to win. Barack Obama published two books shortly before his two elections. "The Audacity of Hope" clearly helped position his candidacy, but his children's book "Of Thee I Sing" probably didn't do much to undermine Mitt Romney in 2012.

(We'll note that a lot of books are written by people who share a name with a presidential contender. This probably isn't that Gary Johnson. And this probably isn't that Rick Perry. And the book written by a Chris Dodd that's at Amazon is very much not that Chris Dodd.)

Carson isn't alone. Candidates for the 2016 race have cranked out a lot of books recently. Not all of these are of the I-am-going-on-book-tour sort; many have less grandiose ambitions. But if anyone knows the value of a book in terms of 1) making money and 2) raising a person's profile, it's Ben Carson. His book "Gifted Hands" helped make him wealthy and well-known.

So what's Carson up to with this hiatus? It's probably pretty simple. He's doing quite well in the polls, for now, and he's at the peak of his popularity. Taking two weeks to do a different sort of appearance that can presumably be paid for from a nonregulated account while making money from doing so doesn't seem like too hard a choice.

In fact, that's a better reason to release a book than the normal reason candidates release books: Book-writers rarely go on to win the presidency. So if you are going to release one right before the primaries, might as well make sure you earn a buck from it.