George Bush has vowed to cast the first veto of his presidency this week if the Senate, as expected, follows the House of Representatives and passes a bill to boost federal funding of stem-cell research.
The key vote was expected last night when the Senate delivered its verdict on three separate bills, the most controversial of which would do away with the limits that the President imposed on stem-cell funding in 2001.
At that time, Mr Bush made clear his fundamental opposition to stem-cell research - thus aligning himself with social conservatives who regard the practice as abortion by another name. However, polls now show that Americans back wider stem-cell research by a two to one margin, and speculation had grown that he was ready to change his mind.
But on Monday, the White House issued a written statement reiterating its opposition to a bill that "uses taxpayers' money to pay for research that relies on the intentional destruction of human embryos" and which "overturns the President's policy that funds research without promoting such ongoing destruction".
Mr Bush's reluctance to use the veto even once in five and a half years in the White House is remarkable. In just a single term, his father issued 44, while Bill Clinton vetoed 38 pieces of legislation while he was in office between 1993 and 2001.
But special factors have applied. Republicans have controlled both chambers of Congress since 2003 and the continuing "war on terror" has made the party less willing than otherwise to confront Mr Bush.
But that long spell of subservience may be drawing to an end, with the approach of November's mid-term elections and the slide in the President's approval ratings to below 40 per cent.
That, however, has not deterred Mr Bush from resorting to the previously little-used practice of signing a bill - for example, the amendment outlawing torture attached to the 2006 Pentagon budget - but adding a so-called "signing statement" saying how he would interpret the new law.
Although at least 60 senators were expected to back the stem-cell measure, it seemed unlikely that it would achieve the two- thirds majority of 67 votes needed to override a veto. The same goes for the House, which in 2005 passed the measure by 238 to 194, more than 50 votes short of the required "super" majority of 290.
But the legislation has struck a powerful chord and stem-cell research is shaping up as an issue in the November elections. It boasts several high-profile supporters, including Nancy Reagan, the widow of the former president Ronald Reagan, who died in 2004 of Alzheimer's disease, and the Senate majority leader, Bill Frist, a heart surgeon, who is likely to seek the Republican presidential nomination.
Speaking in the Senate this week, Arlen Specter, another Republican, who chairs the Judiciary Committee, compared Mr Bush to opponents of Columbus and Galileo, and people who at first rejected electricity, vaccines and rail travel.Reuse content