Bill Frist (R-Tenn.), a renowned heart surgeon before becoming Senate majority leader, went to the floor late Thursday night for the second time in 12 hours to argue that Florida doctors had erred in saying Terri Schiavo is in a "persistent vegetative state."

"I question it based on a review of the video footage which I spent an hour or so looking at last night in my office," he said in a lengthy speech in which he quoted medical texts and standards. "She certainly seems to respond to visual stimuli."

His comments raised eyebrows in medical and political circles alike. It is not every day that a high-profile physician relies on family videotapes to challenge the diagnosis of doctors who examined a severely brain-damaged patient in person. Democrats were quick to note that Frist was getting rave reviews from conservative activists who will play a major role in the 2008 presidential primaries he is weighing.

In addition to the speeches, Frist backed a Senate strategy that threatens criminal sanctions against anyone who keeps Schiavo from attending a Washington hearing next week, to which she and her husband Michael Schiavo were invited early yesterday.

"I suspect that Senator Frist has his eye more on the Iowa caucus than the Hippocratic Oath," said Marshall Wittmann, a senior fellow at the Democratic Leadership Council and former GOP Senate staffer. "This is clearly the politics of the Republican base."

Republican pollster Anthony Fabrizio said Frist will doubtlessly win applause from staunch opponents of euthanasia and abortion, but he may receive a cooler reception from advocates of states' rights and limited federal government. "If you want to confirm your bona fides" with the former group, Fabrizio said, "this is a good way to do it. But while you're pleasing one segment of the party, you may be setting yourself up for trouble with conservatives who say 'we don't want more federal control over this stuff.' "

Some medical professionals questioned the appropriateness of Frist challenging court-approved doctors who have treated Schiavo. Laurie Zoloth, director of bioethics for the Center for Genetic Medicine at Northwestern University, said she was surprised to hear Frist weigh in, given that he has not examined Schiavo. "It is extremely unusual -- and by a non-neurologist, I might add," Zoloth said in an interview.

Were Frist rendering an official medical judgment, she said, relying on an "amateur video" could raise liability issues. After 15 years, "there should be no confusion about the medical data, and that's what was so surprising to me about Dr. Frist disagreeing about her medical status," Zoloth said.

It is not the first time that Frist has created a stir in medical and political circles. In December, on ABC's "This Week With George Stephanopoulos," he repeatedly declined to say whether he thought HIV-AIDS could be transmitted through tears or sweat. A much-disputed federal education program championed by some conservative groups had suggested that such transmissions occur.

After numerous challenges by Stephanopoulos, Frist said that "it would be very hard" for someone to contract AIDS via tears or sweat. The Web site of the Centers for Disease Control and Prevention says: "Contact with saliva, tears, or sweat has never been shown to result in transmission of HIV."

Frist's aides say political considerations played no role in his actions regarding Schiavo. "His interest in this was sparked solely as a medical and human rights matter," said Eric M. Ueland, his chief of staff. "It's time for people to take off the 2008 rose-colored glasses and see Bill Frist for who he really is."

Conservative activist Gary Bauer, who made a 2000 presidential bid, praised Frist's role in the Schiavo case and said he would be surprised if conservatives of any stripe take offense. "I don't think there's any danger on the limited-role-of-federal-government argument," Bauer said, "because protecting life is an issue that transcends federalism."

Still Bauer said, Frist's intervention carries political risks because "the general public has been told she's in a vegetative state," and voters may view his actions as inappropriate meddling. "But I think he and others have been so courageous about this" that people will see them as "willing to go to the mat for one handicapped individual in Florida."

Democratic strategist Jim Jordan offered a much stronger assessment. "It's quackery," he said. "It'd be hilarious if it weren't so grotesque, how his presidential ambitions and pandering to the right wing is clashing with his life's work."

Staff writer Shailagh Murray contributed to this report.

Heart surgeon and Senate Majority Leader Bill Frist (R-Tenn.), left, greets Bobby Schindler, brother of brain-damaged Terri Schiavo in Florida.