That detail helped the issue catch fire on cable TV and inspired protests on Richmond's stately Capitol grounds. By Wednesday, Gov. Robert F. McDonnell had withdrawn his support for the original legislation and left in question the fate of a substitute. McDonnell, a potential Republican vice presidential candidate who a week ago was stumping for former Massachusetts governor Mitt Romney in Michigan, found himself in an unflattering national spotlight. It was a spectacular and unexpected reversal for McDonnell and other Virginia Republicans, who in November's elections grabbed hold of every lever of power in Richmond. But for a governor with national political aspirations, the controversy exploded just as his efforts got underway to help deliver a swing state for his party in this fall's presidential and U.S. Senate contests. Asked about what specifically led to his reversal, McDonnell and his office declined to comment. But legislators and staff members, who spoke on the condition of anonymity to discuss the matter freely, said the governor began having doubts about the legislation last weekend. The unraveling begins The slow-motion unraveling of the original ultrasound bill began weeks ago, when one Democratic senator buttonholed another after the health committee voted to approve it. Sen. George L. Barker (D-Fairfax), who has a background in health care and opposed the measure, knew that in the earliest stages of pregnancy, only a vaginal ultrasound can detect the fetus. Barker pulled aside Sen. Ralph S. Northam (D-Norfolk), a doctor who had served as technical adviser on the bill. Barker asked: Since 90 percent of abortions take place in the first trimester, wouldn't the bill mostly require a more invasive ultrasound, than the ordinary "jelly-on-the-belly" variety. The bill didn't say. Northam said he didn't know, and Barker suggested he check with medical experts. "I said, "You didn't say anything about this," " Barker said of the committee meeting. Northam consulted with medical experts, who confirmed that a vaginal probe would be needed in the early stages of pregnancy. So when the measure came up for a vote in the Senate on Jan. 31, Barker and Northam raised the issue during the floor debate - but delicately. They used the words "transvaginal" and "internal." But they didn't use startling terms such as "vaginal penetration" and "state-sponsored rape," which eventually came to dominate the debate. Mindful of the teenage Senate pages sitting in the chamber, Barker said, they wanted to be sensitive with their language.