For five years, there has been a sustained effort to overturn the limits set by the president. Advocates of federal funding for research on new stem cell lines have made such funding a litmus test for being "pro-science." Prestigious journals like the New England Journal of Medicine give reports on embryo research special consideration for publication. Meanwhile, advocates downplay advances that do not involve embryo destruction. Reversing the Bush policy -- even forcing a veto -- would be the crowning achievement of this campaign. It would create, so the thinking goes, a great election issue: Progressives are pro-cure and pro-science. Bush is not.

But as often happens in politics, when momentum builds for a cause, that cause may already be on the way to irrelevancy. The facts on the ground change. H.R. 810 would fund research on so-called "spare" human embryos. Such embryos, however, offer an inefficient and ineffectual road to medical progress: inefficient, because procuring consent to use leftover embryos is a cumbersome process, and the vast majority of couples who produced them do not want them used for research; ineffectual, because using "spare" embryos does not allow scientists to control the genetic makeup of the stem cells, which is (as they have told us) essential for building useful models of disease and developing rejection-proof therapies.

While the political fight over the "spares" has raged, some scientists seem to have found a better way forward: a way to get the genetically controlled stem cells they need without destroying human embryos. A second Senate bill (S. 2754), cosponsored by Arlen Specter and Rick Santorum (usually opponents in the embryo research debate), would fund and promote such research. These alternative methods are better ethically, because they do not treat developing human life as raw material; better scientifically, because they would provide designer stem cells; and better democratically, because they do not force those who believe embryo destruction is a grave moral wrong to fund it with taxpayer dollars.

The most important arguments for maintaining the Bush policy are moral: The federal government should not be a party to the destruction of nascent human lives. Yes, such embryos might be left over in fertility clinics, but the fact that they are unwanted does not change what they are or give us a license to destroy them. But even for those who are agnostic about the moral standing of human embryos, a policy that encourages the expanded use of federal dollars for research on "spare" embryos makes little sense when more promising alternatives apparently exist.

Of course, we cannot predict the scientific future -- a fact too often ignored by those promising to cure "100 million" Americans if only we funded embryo research without limits. Even the most promising scientific alternatives are speculative. But this much we do know: Destroying more "spare" embryos is unlikely to advance stem cell science significantly. Rather, using federal dollars to fund such research will only lead to demands that further ethical lines be crossed. When using the "spares" doesn't produce results, the demand will be to fund the creation and destruction of embryonic human clones, an even more damaging leap into the brave new world.

We should instead be establishing barriers to such a world. And fortunately, the Senate is poised to consider a third bioethics bill (S. 3504) prohibiting "fetal farming." Such an idea is not science fiction. Scientists could plausibly say that we need to encourage the gestation of human embryos to later developmental stages, when potentially more useful stabilized stem cells could be obtained and organ primordia could be "harvested." Establishing a preemptive moral limit on such schemes would embody an important truth: There are some things we should never do, even in the name of progress. The moral history of mankind, as Paul Ramsey once said, is more important than its medical history.

So: no funding for the destruction of "spare" embryos; generous funding of alternative methods of producing embryonic-like stem cells; and banning "fetal farming." This outcome would hardly prevent every abuse -- leaving human cloning and the new eugenics entirely unregulated. But after five years of difficult debate, we may achieve in the next weeks a decent outcome -- for now.

--Eric Cohen directs the Bioethics and American Democracy program at the Ethics and Public Policy Center and is editor of The New Atlantis.  William Kristol is editor of the Weekly Standard.