President George W. Bush’s veto on Wednedsay of embryonic stem cell legislation marks a turning point for a president who has until now been able to dictate what the Republican-controlled Congress has sent to the White House for him to sign.

Mr Bush’s veto – the first in his five and half years in office – sent the bill to expand federal funding of the controversial research back to the House of Representatives, where backers of the measure were not able to muster the two-thirds majority needed to override his decision.