If you can count to four—and know that four is less than five—then you can understand why South Dakota’s new law banning almost all abortions is a mistake for the pro-life cause. Antonin Scalia, sure he’d go for this. Clarence Thomas, too. And maybe John Roberts and Samuel Alito, the new guys in the black robes, although we don’t know for sure.

But that’s it. And since four isn’t five, a majority of justices on the Supreme Court will affirm—yet again—the current unlimited abortion license when eventually they hear the South Dakota case. And every time the high court sets down another decision declaring abortion a fundamental constitutional right, the burden of overturning the court's now 33-year-old decision in Roe v. Wade ruling that permitted unrestricted abortion grows heavier.

The pro-life cause doesn’t need the South Dakota law right now; we need, in fact, not to have the South Dakota law, or the similar Mississippi bill that just failed to pass, or any of the kindred proposals being floated in other states.

Mainly, that’s because Roe v. Wade is already in serious trouble. Is there a lawyer in the United States who actually believes Roe was a well-reasoned legal decision? There’s no doubt that the result still has plenty of supporters. But it’s an open secret that the grounds offered for the decision—an amorphous right to privacy—are an embarrassment in constitutional law, even for those who want legalized abortion. Meanwhile, the health-of-the-mother clause in Roe’s companion decision, Doe v. Bolton, has proved a litigation morass, and pro-lifers' attempt to shift the right to abortion onto firmer ground with Casey v. Planned Parenthood in 1989 produced only the famous “mystery passage”: “At the heart of liberty is the right to define one’s own concept of existence, of the universe, and of the mystery of human life. Beliefs about these matters could not define the attributes of personhood were they found under the compulsion of the state.” It became perhaps the single most mocked jurisprudential dictum of modern times. Short of catastrophe, the Supreme Court's landmark abortion decisions are all ultimately headed for the shredder.

Unfortunately, the South Dakota bill has the chance to be exactly such a catastrophe for the pro-life cause. For several years, the strategy of the pro-life movement has been to chip away at the Supreme Court's abortion decisions: exposing their contradictions, describing their flaws, and marking their inconsistencies. By enacting an in-your-face challenge to Roe in the form of a ban on all abortions except to save the life of the mother, South Dakota has invited the court to cobble up yet one more justification for a putative constitutional right to abortion—which will then require yet more years of pro-life work to undo.

Meanwhile, the usual abortion-promoting groups are already using the legislation to raise funds and rally the troops.

The media have generally gone along with the abortion activists’ line that equates the sweeping South Dakota bill with every other kind of opposition to abortion, such as opposition to late-term abortion or abortion as birth control. And that, too, makes the battle more difficult. If Justice Anthony Kennedy, generally a Roe supporter, was serious in his previous opinions when he said that Roe permits legislators to restrict third-trimester abortions, then there may now be the five-vote majority needed to assert that the right to abortion does not trump every other consideration—and that abortion is therefore, in principle, subject to restriction and regulation. With that crack in the rock that rolled over us in 1973, there is an opportunity to start breaking off more pieces—or so the argument goes—until Roe is finally reduced to rubble. But if the abortion activists and their supporters in the press can successfully equate restrictions on, say, partial-birth abortion with an outright ban on nearly all abortions as in the South Dakota law, the crack gets harder to open.

I grew up on those windy South Dakota plains, and I know those people—descendents, mostly, of the kind of Scandinavian immigrants Ole Rolvaag described in his classic 1927 novel of the Dakotas, Giants in the Earth. There’s hunger in places like South Dakota for something to happen. President Bush forgot during the brief Harriet Myers imbroglio that changing the Supreme Court was the election issue for a large number of people who voted for him in 2004. And now, with Roberts and Alito on the Court, those people want to see results. The base is worked up, the abortion-supporting Democrats looked feeble and stupid during Alito’s confirmation hearings, and for the first time since the Webster decision in 1989, the end of Roe is actually imaginable.

Not certain, and maybe not even likely. But that it should be even imaginable is huge change: For the first time in many people’s adult life, we can picture a genuine path for returning abortion law to the states. So it’s not really surprising that the national pro-life groups can’t keep tight control of the movement. Down at the roots, the grass is on fire.

But after all the careful work the pro-life movement has done to set in motion the analysis by which Roe can be chipped away, the South Dakota legislation is simply and clearly a tactical error.