I take Jon Huntsman's view that "re-defining marriage would be impossible" to be a theological, not a political statement. Because politically, same-sex marriage cannot be impossible when it has already been in existence for many years in several states. My civil marriage, licensed both in Massachusetts and Washington DC, is not "impossible", although, like all marriages, it may seem so from time to time. It is an empirical, legal and political fact.
What Huntsman presumably means is that in his faith tradition, a same-sex marriage would be impossible. Here is what the LDS Church believes about marriage:
In the marriage ceremony a man and a woman make covenants to God and to each other and are said to be sealed as husband and wife for time and all eternity. The Latter-Day Saint distinguishes itself on this point…
In the current LDS Church, both men and women may enter a celestial marriage with only one partner at a time. A man may be sealed to more than one woman. If his wife dies, he may enter another celestial marriage, and be sealed to both his living wife and deceased wife or wives. Many Mormons believe that all these marriages will be valid in the eternities and the husband will live together in the Celestial Kingdom as a family with all to whom he was sealed.
But it does seem plenty odd, don't you think, that a leading Mormon would argue that marriage cannot be redefined, when his own church redefined it well over a century ago to outlaw polygamy, previously one of the LDS church's deepest doctrines? If you can redefine it from that, why would subsequent redefinitions – such as allowing inter-racial marriage – not be permitted?
More to the point: if Huntsman is referring to his religious position, wouldn't that bar all non-Mormons from marriage as Mormons understand it? No non-Mormon can be married in a temple. Even non-Mormon parents of the groom or bride are not allowed. So if marriage cannot be redefined outside Mormon grounds, does Huntsman believe that anyone apart from Mormons are actually, you know, married?
The Dish 