Mississippi votes today on a referendum that could have political implications far beyond the Magnolia State. (Ed, that reference is for you.)

The state’s voters will consider Initiative 26, which is the latest and most extreme measure in a growing effort to outlaw abortion. Instead of chipping away at Roe v. Wade, the referendum, which enjoys the support of Mississippi’s leading politicians, strikes at the heart of that decision. It centers on a new approach to expand legal protections beyond the fetus to something called, “personhood,” which under this ballot measure’s definition begins at the moment of conception.

The politically interesting consequence of the emerging “personhood” movement — there have been other ballot measures in other states — is not that it would make abortion a crime even in cases of rape and incest, but what it could do to criminalize certain popular forms of birth control.

(Disclosure: I and my firm have worked for pro-choice and birth control advocates.)

To review high school biology, conception occurs when an egg is fertilized, but the abortion debate, until now, has centered on a more common, if still controversial, definition of when life begins: when the fertilized egg attaches to the uterine wall and starts growing. About half of fertilized eggs naturally do not “make it” to this stage of fetal growth. By extending legal protections to the zygote, the referendum’s logic criminalizes the morning after pill, the IUD and possibly the pill. Finally, by defining an embryo as a “person,” the prospective law would make in vitro fertilization much more difficult. Perversely, an amendment ill-designed to protect life would deny it to those individuals and families struggling with fertility.

So why does this matter for 2012? While the economy is dominant, the personhood movement exposes a strain within the Republican Party that appalls the vast majority of voters and is the last issue most Republicans want to talk about. The polls in this country may be mixed on the abortion question, although there is very little support for making it illegal without exception, but the polls are decidedly very certain when it comes to contraception. A vast majority from all demographics and varied religions backgrounds support it.

I would not want to have to defend this referendum if I were running a presidential campaign or a state-wide race in all but a handful of states. It is a potentially very powerful new issue in the presidential campaign, and lest anyone think it is confined to the fringe, Mitt Romney’s budget package eliminates Title 10 funding, which provides birth control to 5 million women.

Several times in our recent history, restrictions on abortion have played a central role in elections in swing states such as New Jersey and Virginia. Now access to birth control could be next year’s social wedge issue.