Rick Santorum, in an interview some years back:
"Every society in the history of man has upheld the institution of marriage as a bond between a man and a woman. Why? Because society is based on one thing: that society is based on the future of the society. And that's what? Children. Monogamous relationships."
The comment has mostly been criticized in the context of the dispute over same-sex marriage. What struck me was the profound historical ignorance it implied, assuming Santorum actually believed what he said.
One can argue about whether or not any historical society had something equivalent to same-sex marriage—but Santorum included in his description of what every society was based on "monogamous relationships." Monogamy is, historically speaking, more common than polygamy, but polygamy was an accepted form of marriage not only in the Islamic world (where it still is) and in China through most of its history—two of the world's great civilizations. It was also an accepted practice in Old Testament judaism, the society on which all three of the major monotheist religions are based.
Santorum does not, however, have any monopoly on historical nonsense.
Gingrich: "I think Jefferson or George Washington would have strongly discouraged you from growing marijuana, and their techniques for dealing with it would have been rather more violent than the current government."
Most of the current crop of candidates could be excused for that one, but Gingrich, before he got into politics, was a professional historian and has written alternate history novels set in 19th century America. Yet he apparently does not realize that marijuana only became illegal in the U.S. in the 20th century. Or that, in the 18th century, hemp was an important commercial crop—and both Washington and Jefferson grew it.
Alternatively, and perhaps more plausibly, he doesn't actually connect what he says with what he knows.
To be fair, it is not only Republican candidates who appear to be strikingly ignorant of historical facts. It was, after all, our current Vice-President who, in a televised interview, claimed that:
“When the stock market crashed, Franklin D. Roosevelt got on the television and didn’t just talk about the, you know, the princes of greed.”
Thus demonstrating that:
1. He didn't know who was president in 1929.
2. He thought television was widely available in 1929—ten years before the first presidential speech to be given on television.
Readers are invited to provide additional examples.