Congress is moving to expand funding for research, but President Bush promised a veto.
In a presidency marked by partisan polarization, this may go down as the week of the ascendant moderates - first on judicial nominees and now on embryonic stem cell research.
The stem-cell legislation, passed by the House with a bipartisan majority and headed for likely passage in the Senate later this spring, would expand federal funding for research, a position President Bush vehemently opposes. He has promised his first presidential veto, after an extraordinary stretch without wielding that pen.
And even though Bush has the strong backing of religious- conservative leaders, who believe human-embryo research entails the taking of a human life, a majority of the public - including some conservatives in the House and Senate - believe there is a higher moral value at stake: that this research could someday improve or save the lives of people with diseases the medical world considers incurable.
Bush, who held an event in the White House on Tuesday with children who had been adopted as frozen embryos, has laid down his marker. This issue is a cornerstone in his campaign to promote a "culture of life."
Some moderates are hoping to draw the president into a compromise, given that the margin of House passage, 238 to 194, fell well short of the two-thirds majority needed to override a veto. One possible compromise floated by moderate House leaders would be to push forward the cutoff date for eligible stem-cell lines. In August 2001, when Bush announced federal funding for stem-cell research, he said only existing lines could be used. Many of those have proved unusable.
But social conservative leaders flatly oppose any accommodations that would allow federal funds to be used in the destruction of additional embryos.