The Supreme Court unnecessarily returned to the politically charged area of abortion this week, hearing arguments in a case testing some of the core principles of Roe v. Wade and the court's own credibility as an institution removed from politics.

At issue, once again, is a deceptively broad ban on so-called partial-birth abortions. The court struck down a similar measure just six years ago, but since then two new justices have arrived. In the interest of women's privacy and health — and in defense of the court's own reputation — the justices should strike down this far-reaching assault on reproductive freedom.

In 2000, the court struck down a nearly identical Nebraska law for essentially two reasons. It found that the law's imprecise language applied not just to a single late-term abortion method — as the ban's supporters claimed — but would criminalize other common abortion procedures that are constitutionally protected. The court also ruled that the law was unconstitutional because it provided no exception to protect a woman's health.

In a cynical move in 2003, Congress passed a law remarkably similar to the one the court had just struck down — with a definition of the procedures it was outlawing about as sweeping as Nebraska's. Defying the Supreme Court, moreover, Congress refused to include an exception for protecting the health of the woman. Instead, it simply made the medically inaccurate assertion that the ill-defined procedure it outlawed was never necessary to preserve a woman's health. Every lower federal court that has considered the Congressional ban has held it to be unconstitutional.

If Justice Sandra Day O'Connor, who cast the deciding vote in 2000, had not retired, it is highly unlikely the court would have agreed to entertain this rerun. But without her, it is not clear that there are still five votes to defeat this assault on Roe , or to uphold the bedrock requirement that abortion restrictions have an exception for protecting a woman's health.

It seems unlikely that Chief Justice John Roberts or Justice Samuel Alito will provide the fifth vote. That means that Justice Anthony Kennedy, the current swing justice, is likely to decide this case. In 2000, Justice Kennedy joined those who would have upheld the Nebraska law. But at oral argument his questions suggested that he may take issue with Congress's assertion that the ban would not put women's health at risk — an encouraging sign.

Even justices who oppose abortion rights need to be concerned about that. They also need to worry about how the court will look if the recent change in its membership produces a starkly different result on an issue so vital to women's privacy and health.

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