MSNBC host Lawrence O'Donnell explains that contrary to what Tony Perkins and Mitt Romney say, the definition of marriage has changed quite a few times over the years.
Social conservatives like Perkins, the president of the Family Research Council, have grown accustomed to claiming that allowing same-sex couples to marry is "redefining" marriage and that redefining it alone is a radical step.
But marriage has actually had to be legally redefined several times — to allow interracial marriages, for example. Or to ban polygamy. O'Donnell points out that Perkins and other religious aficionados should know this well if they read their Bibles.
Watch the history lesson below.