Mayor Giuliani’s rift with his family has resurfaced with the news that his 17-year-old daughter, Caroline, signaled, albeit electronically, her support for Senator Obama for president.

Ms. Giuliani reportedly listed herself as a member of an online group Mr. Obama created to drum up support for his presidential bid. But the soon-to-be Harvard University freshman removed her name from the pro-Obama group after an online magazine, Slate, contacted her about it; a spokeswoman who represents her was quoted as saying her membership in the group was not meant as an endorsement.

The posting on Facebook, a social networking site, comes several months after Mr. Giuliani’s son, Andrew, attracted national attention by publicly saying that he was estranged from his father, who is seeking the Republican nomination for president. Both of Mr. Giuliani’s children have aligned themselves with their mother, Donna Hanover, since she and the former mayor split. Andrew Giuliani indicated that his father’s current wife, Judith Nathan, is the source of the conflict.

Political analysts said that while they do not expect yesterday’s snafu to be especially damaging for Mr. Giuliani’s campaign, it will remind voters of the mayor’s turbulent family life.

Political historians said few modern day presidential candidates have had a family member break ranks with them to support someone else. President Reagan’s daughter, Patti, whose leanings were reportedly far more liberal than those of her Republican father, had public conflicts with her family. And in 2004, Reagan’s son, Ron, appeared at the Democratic National Convention, but that apparent rejection of his father’s political party came after his father’s death.

A political science professor and presidential historian at Hunter College, Andrew Polsky, said Ms. Giuliani’s Facebook posting would have no serious consequences for the Republican front-runner, largely because the country already knows he does not have a picture-perfect family. “I don’t think that Americans expect anymore that presidential families are all sweetness and light,” he said. “We’ve haven’t had that for quite a long time.” The mayor’s daughter never intended her membership in the Obama group as any kind of endorsement, a spokeswoman for Ms. Giuliani said yesterday, according to the Associated Press. A Republican strategist and former assistant to Reagan, Edward Rollins, said “signing up on Obama’s Facebook group is not a full-scale endorsement in the same way that standing on the steps of City Hall is.”

“My sense is that she is a 17-year-old kid who obviously has issues with her father that don’t have anything to do with politics,” he said. He called the issue “innocuous” but said it does draw attention away from Mr. Giuliani’s policy messages and toward his family discord.

When asked about the incident in Iowa yesterday, Mr. Giuliani declined to comment, saying only: “My daughter I love very much. I have great respect for her, and I’m really proud of her. And I don’t comment on children because I want to give them the maximum degree of privacy.”

Ms. Giuliani’s Facebook profile is available only to those who attend or attended her alma mater, Trinity High School on the Upper West Side, and Harvard. According to Slate, she also used a variation on her name on her profile; she reportedly has used her mother’s last name, Hanover, instead of Giuliani in the past.

Still, the incident highlights just how quickly an online comment can become a national campaign issue. Other prominent New York political children, including Mayor Bloomberg’s daughter Emma and Senator Schumer’s daughters, Jessica and Alison, also have Facebook profiles on the Harvard network. And Mr. Giuliani’s two leading rivals for president — a former Massachusetts governor, Mitt Romney, and Senator McCain of Arizona on the Republican side, and Senators Clinton, Edwards, and Obama on the Democratic side — all have Facebook profiles set up. The former mayor does not.