For the first time in his five and a half years in office, President Bush last night vetoed a piece of congressional legislation. To date he has signed 1,116 laws into force. The bill would have enabled federal funding to be released for stem cell research, over-riding Mr Bush's executive order of August 2001. There have been major advances in scientific discovery since then, leading to a deeper understanding of the ethical issues at stake among US researchers, legislators and the public at large. These were fully aired in the congressional debates, but Mr Bush has chosen to stick by the line he adopted five years ago.
In doing so he holds to a commitment made to right-wing conservatives that he would protect and defend all human life, including the human embryos from which stem cells derive. The 400,000 embryos involved are frozen in fertility clinics across the US; most of them will be routinely destroyed, having been produced to address the problem of childlessness and then become redundant to that task. The scientific techniques of implantation have expanded extraordinarily rapidly, throwing up these moral and legal dilemmas in their wake.
Mr Bush argues that allowing stem cell research on such embryos is tantamount to destroying human life. His argument resonates with conservative Christians, one of his principal support bases. But other members of his political coalition have shifted ground in response to changing evidence, circumstances and argument over the last five years.
The majority Republican leader in the Senate, Bill Frist, supports this bill. Another Republican senator, Arlen Specter, compares its opponents to those who imprisoned Galileo or laughed at electricity. Their arguments are based on research advances on Alzheimer's and Parkinson's disease and diabetes using stem cells, which demonstrate great promise. The voluntary, donated aspect of their provision and the fact that most of the embryos produced will otherwise be destroyed, together with this proven scientific advance, have convinced 75 per cent of US citizens to support the bill, according to the latest opinion polls.
They are right to judge the scientific and medical potential of this research according to its potential human benefits. It is better to compare the use of tissues from such embryos to the practice of organ transplantation with a life-affirming purpose, rather than to clinical abortion. Such judgments are difficult and heavily contested. They should take full account of deepening scientific understanding to reach ethical and legal conclusions.