But if it centers on the fetus or the details of the procedure itself, opponents are in a better position.
Particularly in the early years after Roe v. Wade, "there was too much abstract debate," said Marjorie Dannenfelser, president of the Susan B. Anthony List, which promotes female candidates who are against abortion. "We have found that the more specific you are about the thing you are talking about, the more public opinion will move your way."
Both principles have been at work over the past few election cycles.
In last year's election, Republicans lost two U.S. Senate races in large part because GOP candidates made insensitive comments about pregnancies that result from rape. Democrats rallied their base by accusing Republicans of waging a "war on women" with their efforts to defund Planned Parenthood and through legislation, in states including Virginia, that would require women seeking abortions to have intrusive and medically unnecessary transvaginal ultrasounds.
More recently, abortion opponents — who saw their ranks increase in state legislatures after the 2010 midterm elections — seem to be gaining ground.
In the first six months of this year alone, legislatures in 17 states placed 43 new restrictions on the procedure, according to figures compiled by the Guttmacher Institute, an abortion-rights advocacy organization that produces data cited by both sides in the debate.
The bill under debate by the Texas Legislature falls into the middle of abortion's political crosscurrents.
The bill gained national attention when state Sen. Wendy Davis of Fort Worth waged a 13-hour filibuster against it in the waning hours of the legislature's previous session.
One of the provisions — banning abortion after 20 weeks' gestation — is a move that polls favorably. Currently, 41 states impose a ban at some point during a pregnancy, eight of them at 20 weeks after fertilization. Last month, the U.S. House also passed a 20-week ban, largely along party lines, but it appears to have no chance in the Senate.