Michele Bachmann famously called America under President Obama a “nation of slaves.”

Then she got into trouble for suggesting that the founding fathers "worked tirelessly to end slavery." (She meant John Quincy Adams, the abolitionist president who was 8-years-old when the Declaration of Independence was signed).

Today the Minnesota Republican is again under attack on slavery for signing an Iowa Christian group’s “Marriage Vow” that reads in part:

“Slavery had a disastrous impact on African-American families, yet sadly a child born into slavery in 1860 was more likely to be raised by his mother and father in a two-parent household than was an African-American baby born after the election of the USA's first African-American President.”

The pledge, which she is the only presidential candidate to sign so far, also commits her to banning porn and same-sex marriage. Not a surprise.

But to Bachmann’s detractors , the language on slavery represents a further misreading of history. Apart from the intimation of better conditions in the old antebellum South, the vow seems to overlook a brutal historical record of African-American slave families being broken up for sale.

It’s not just Bachmann who might have to own The Family Leader’s traditional marriage vow, which also calls for the rejection of Sharia Islam, the recognition that married people enjoy “better sex,” and that “robust childrearing and reproduction is beneficial to U.S. demographic, economic, strategic and actuarial health and security.”

Bob Vander Plaats, a conservative evangelical leader who was state chair of Mike Huckabee’s presidential campaign in the 2008 Iowa caucuses, has let it be known that his group will not support any candidate who declines to sign.

So far, there’s been no word from the campaign of former Minnesota Gov. Tim Pawlenty, who desperately needs a good showing in Iowa.