On Thursday, surrounded by a group of female anti-abortion activists, Sen. Lindsey Graham introduced an anti-abortion bill passed months ago in the House for Senate consideration. The bill would ban abortions after 20 weeks, and proposes an alternative to the constitutional standard set by Roe v. Wade to determine the legality of the procedure. It's called the "Pain-Capable Unborn Child Protection Act," and it relies upon a scientifically-challenged assertion that fetuses can feel pain by, at the latest, 20 weeks of development.

When it was introduced in the House by Rep. Trent Franks last spring, anti-abortion legislators hoped to capitalize on the outrages of Kermit Gosnell's Philadelphia clinic to sway public opinion towards more restrictive anti-abortion laws. The bill passed in the Republican-controlled House in June. It includes exceptions to save the life of a mother, or in the case of a properly reported rape or instance of incest. It does not contain exceptions for severe fetal anomalies detected near or after the 20-week limit. In his introduction today, Graham argued that the bill was not about politics, but about saving lives: 

"We are choosing today to speak up for all babies at 20 weeks, and trying to create legal protections under the theory that if you can feel pain the government should protect you from being destroyed by an abortion, which I imagine would be a very painful way to die."

The bill would only directly impact a tiny percentage of abortions performed in the U.S. as it stands: Just 1.3 percent of legal abortions occur after 21 weeks, according to statistics from the CDC. Most women who undergo the procedure do so in the first eight weeks of pregnancy, and 91 percent of abortions in the U.S. occur before the 12th week of pregnancy. And while the idea of limiting late-term abortions draws a slight majority — 55 percent — of support in polling, a simple limitation on abortions after 20 weeks is not the point (or the most likely effect) of the bill if it were to become law. That would be its challenge to current constitutional precedent. 

Currently, based on the precedent set in Roe v. Wade, women have the constitutional right to an abortion before a fetus is viable, which is more or less determined to be at about 24 weeks into the pregnancy. The current bill would instead use a standard popular among anti-abortion activists, of when a fetus can, in theory, feel pain. Similar "pain capable" bills, including one from Rep. Franks's home state of Arizona, have passed several state legislatures, often to face court challenges for exactly this reason. The hope among those who would like to discard or limit the Roe v. Wade protections is that one of those challenges leads to a favorable ruling by the Supreme Court on the new "pain" standard. If that happened, the "pain" standard could justify earlier and earlier bans on the procedure, based on the arguments by a handful of anti-abortion medical professionals who promote the alternative standard. Those experts believe that fetuses can feel pain at as early as eight weeks

Despite Graham's statement today that the "scientific evidence is overwhelming" in support of the so-called "pain capable" theory, the evidence seems to be overwhelmingly against Graham's claim. Most studies and scientific reviews on the subject (including this one, and this one) note that the nerve circuitry required to feel pain don't develop fully until about 24-26 weeks, or around the time the current Roe v. Wade precedent kicks in to limit abortion procedures. In a statement, the American Congress of Obstetricians and Gynecologists explained that scientific evidence indicates that it is very unlikely a fetus would perceive pain at 20 weeks, despite the fetal responses to stimuli cited by Graham and other anti-abortion activists as their scientific justification for the limitation. 

But Graham's bill is unlikely to be the one that changes the U.S.'s approach to abortion limitations, as the 20-week bans are already playing out individually in the states. The bill probably won't pass the Democrat-controlled Senate. And even if it did, President Obama has already promised a veto.