Much time is spent during abortion debates on the imputing and impugning of motives. Without it, coverage of the Texas legislative battle over late-term abortion, for example, would consist mainly of blank pages and dead air.
But political outcomes are not always reducible to the intentions of the winner. Results are often influenced by deeper trends that neither side of a debate can do much to change or control.
The national abortion settlement declared by Roe v. Wade -- rooting a nearly unrestricted right to abortion in the right to privacy -- has been unstable for 40 years. The reason is a tension between the state of the law and a durable public consensus that human life has an increasing claim on our sympathy as it develops. This view does not reflect either pro-life or pro-choice orthodoxy. But it predicts a more sustainable political resolution.
The media have a slothful tendency to place Americans into rigid categories of pro-life and pro-choice.
The reality is more complicated. A 2011 Gallup poll found that 79 percent of people who describe themselves as pro-choice support making abortion illegal in the third trimester.
"One of the clearest messages from Gallup trends," concludes Gallup's Lydia Saad, "is that Americans oppose late-term abortion." Saad adds: "A solid majority of Americans (61 percent) believe abortion should generally be legal in the first three months of pregnancy, while 31 percent disagree.
However support drops off sharply, to 27 percent, for second-trimester abortions, and further still, to 14 percent, for third-trimester abortions. Gallup has found this pattern each time it has asked this question since 1996, indicating that Americans attach much greater value to the fetus as it approaches viability, starting in the second trimester."
An opinion this consistent and nearly universal must be based on something. The late political scientist James Q. Wilson gave the most persuasive explanation.
In his 1994 essay, "On Abortion," he argued bluntly that "people treat as human that which appears to be human; people treat as quasi-human that which appears quasi-human." Sympathy, in his view, grows with resemblance. This explains why the miscarriage of an embryo is (generally) treated differently than the death of a newborn. It is also the reason, according to Wilson, that we recoil from "the thought of killing an infant that does not differ from the newborn in any respect other than that it receives oxygen and food via an umbilical cord instead of through its nose and mouth."
"Life emerges," said Wilson, "or more accurately, the claims that developing life exert upon us emerge, gradually but powerfully." As a fetus becomes more recognizably human, it invokes "attachment that is as natural as any sentiment that ever enters the human breast." Wilson placed the decisive stage of development, as many Americans seem to place it, at 10 to 12 weeks of gestation. Wilson was broadly criticized, by both pro-life and pro-choice advocates, for attempting to turn sentiments into principles. As a moral matter, I share that criticism.
His gradations strike me as ethically arbitrary, and even universal opinions do not add up to moral rules. But Wilson's theory of "natural moral sentiments" on abortion does seem to describe the way most Americans think about this issue. Which makes it politically predictive.
If Wilson's description is correct, pro-life advocates are unlikely to secure legal limits on abortion during the first trimester -- the period in which most abortions actually take place.
At some point, after late-term abortions are restricted, legislative approaches will become unproductive, and persuasion and the provision of alternatives to abortion will become the main avenues of activism.
But because the Supreme Court imposed a national settlement at odds with natural sentiments, pro-choice advocates are currently on the defensive. Their political challenge is to prevent the working of politics. Their real opponent is democracy, as state after state considers late-term abortion restrictions.
We have some models of what happens, even in very liberal societies, when public views prevail on abortion.
Across most of Western Europe, abortion is legal during the first trimester but heavily restricted later in pregnancy -- after the 14th week in France, Germany and Spain. These limits are not a violation of liberal principles but a recognition that the inherent violence of late-term abortion is at odds with liberal principles.
A Wilson-like settlement on abortion in America would be unsatisfying to many. But it would have the virtue of being sustained by consensus, not imposed by fiat.
Email Michael Gerson of The Washington Post at email@example.com.