Q&A: The US debate over stem cells

Mr Bush has used the presidential veto twice to block stem cell bills

President George W Bush has vetoed legislation that would have expanded publicly funded embryonic stem-cell research.

The bill was passed by the Democrat-controlled Congress in June 2007 despite Mr Bush's threat to block it.

Democratic leaders in Congress are expected to try to gain the two-thirds majority needed to override the veto - Mr Bush's third while in office and his second involving stem-cell research.

The issue has provoked an emotional debate between those who say the research is vital for medical progress, and those who say it destroys human life.

This is how the stem cell debate currently stands in the United States:

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What's the latest on the stem cell debate in Congress?

The bill vetoed by President George W Bush on 20 June 2007 would have allowed more federal money to pay for research on embryonic stem cells.

The Democratic-controlled House had voted by 247 to 176 in early June to pass the legislation and send it to Mr Bush's desk.

It was approved by the Senate in April with a majority of 63 to 24 - just short of the two-thirds required to override a presidential veto.

The Democrats are expected to bring back the bill in one form or another, although they admit they are short of the numbers needed to overturn the veto in both Houses.

Their aim is to keep the legislation - which polls suggest is supported by 60% of American people - in the spotlight.

The Democrats promised to push the expansion of stem-cell research when they took control of the US Congress in the 2006 mid-term elections.

Supporters predict that the debate will be an issue in both the presidential and Congressional elections in 2008.

Some Republicans have backed the bill, although many in the party usually oppose anything which might legitimise abortion.

What has Mr Bush said on the matter?

While he is a strong supporter of adult stem-cell research, Mr Bush says using material from human embryos is a different matter.

Vetoing the latest bill, he said: "If this legislation became law, it would compel American taxpayers for the first time in our history to support the deliberate destruction of human embryos.

"I made it clear to Congress and to the American people that I will not allow our nation to cross this moral line."

He exhorted scientists to "pursue the possibilities of science in a manner that respects human dignity and upholds our moral values".

At the same time, Mr Bush issued an executive order encouraging scientists to pursue alternative ways to obtain stem cells which would not harm human embryos, such as from amniotic fluid, umbilical cords and adult skin cells.

Back in 2001, the president declared federal funding would be available only for research using existing stem cells - meaning that no new lines could be created, whether from existing embryos or cloned embryos.

What do his opponents say?

Supporters of embryonic stem cell research make a case for "respecting life" by using the technology to try to find cures for diseases such as Parkinson's, diabetes and cancer.

The late Christopher Reeve was a vocal advocate of stem cell research

While acknowledging the need for rigorous ethical oversight, some argue the current restrictions are ideologically driven.

Democratic Senator Hillary Clinton, a 2008 presidential hopeful, said in response to Mr Bush's veto: "This is just one example of how the president puts ideology before science, politics before the needs of our families."

There is no law against private stem cell research in the US, and research is moving ahead not just outside the country, but in states like California.

US scientists have complained that the embryonic stem cell lines established before the ban are now becoming unusable.

Why is the row so politically charged?

There are religious and social conservatives who oppose abortion and consequently the destruction of embryos required for stem cell research. Many of these are also supporters of Mr Bush.

But the president has to carry off a delicate balancing act, seeking to placate these supporters without appearing to stand in the way of research or against the wishes of secular Republicans.

High profile advocates of stem cell research have helped thrust the debate into the spotlight.

The death of former Superman actor Christopher Reeve - a prominent advocate - generated great interest in the issue.

Campaigning by other famous names like Michael J Fox and Nancy Reagan has kept it in the public eye.

Mrs Reagan argues that Alzheimer's - the disease from which her late husband, President Ronald Reagan, suffered - could be helped by stem cell research.