But by invoking the sexual orientation of the vice president's daughter, the Democratic candidate unleashed a rhetorical tempest on issues as diverse as the morality of gay marriage, the place of family members in political discourse and the roots of human sexuality.
Anger among Bush campaign officials and supporters mounted Thursday as Cheney called himself "a pretty angry father" and Kerry "a man who will do and say anything to get elected." Lynne Cheney, his wife, said Kerry was "not a good man" and accused him of a "cheap and tawdry political trick."
But Kerry and his supporters responded that Cheney had been first to discuss his daughter in relation to the issue of gay marriage, at a town hall in August. Elizabeth Edwards, wife of Democratic vice presidential candidate John Edwards, said the vehemence of Lynne Cheney's response "indicates a certain degree of shame with respect to her daughter's sexual preferences."
A number of gay rights activists said they thought many Republicans were betraying their discomfort with the issue. They pointed out that Mary Cheney had been open in political and business endeavors about her sexual identity for years.
"It's as if John Kerry had said Mary Cheney was an ax murderer or something," said Cheryl Jacques, president of the Human Rights Campaign, a gay civil rights organization. "The response belies the fact that the extreme right thinks that it is a bad thing that Mary Cheney is gay."
But Michele Ammons of the Christian Coalition of America, said the real outrage was Kerry's "infringement into a personal family matter."
"I think this is going to snowball, and he's going to have to apologize."
The controversy grew out of Kerry's response to a question by debate moderator Bob Schieffer of CBS News. Schieffer told Kerry and President Bush that he understood they both opposed gay marriage but wondered how they arrived at that position. He asked: "Do you believe homosexuality is a choice?"
Bush responded, "I just don't know. I do know that we have a choice to make in America, and that is to treat people with tolerance and respect and dignity." He added that he had proposed a constitutional amendment to define marriage as between a man and woman because he was concerned that activist judges were defining marriage.
Asked for his response, Kerry said: "We're all God's children, Bob. And I think if you were to talk to Dick Cheney's daughter, who is a lesbian, she would tell you that she's being who she was; she's being who she was born as. I think if you talked to anybody, it's not choice."
Following the debate, television commentators across the political spectrum chastised Kerry as "out of bounds."
Fox News analyst Morton Kondracke noted Wednesday that Edwards had a week earlier raised Mary Cheney's sexual orientation in his debate with Cheney. "Kerry repeated it tonight, which I think is totally underhanded," Kondracke said, calling the Democrat's statement "the outing of Dick Cheney's lesbian daughter."
Rich Bond, chairman of the Republican National Committee when Bush's father ran for reelection in 1992, said Kerry was "an utter lowlife for going after Mary Cheney like that."
"I was watching the debate last night with 10 Republicans, and they were just stunned," Bond said.
If Democrats wanted to drive conservatives away from the Republican ticket, Bond said, they instead had "the absolute opposite effect of pissing off Republicans like myself beyond belief."
Campaign officials said that Mary Cheney had no intention of commenting on the matter.
Campaigning in Las Vegas on Thursday, Kerry released a statement saying of the episode: "I love my daughters. They [the Cheneys] love their daughter. I was trying to say something positive about the way strong families deal with this issue."
Appearing on MSNBC's "Hardball With Chris Matthews," Edwards said he and Kerry had tried to put "a personal face on an issue that has been used to divide this country."
Several Democrats noted that it was Cheney who first spoke about his daughter, when he was asked in August about gay marriage at a campaign stop in Davenport, Iowa. "Lynne and I have a gay daughter, so it's an issue that our family is very familiar with," Cheney said, explaining that he opposed Bush's call for a constitutional amendment to ban gay marriage.
Cheney also made no objection last week in the vice presidential debate when Edwards complimented his "wonderful" willingness to talk about his daughter's sexual orientation.
Before joining her father's vice presidential campaign in 2000, Mary Cheney was the Coors beer company's liaison to gays and lesbians. She helped the company improve its image, getting Coors to provide financial support to a number of gay organizations and traveling to gay bars, where the brewery sponsored an "International Mr. Leather" competition.
After her father was elected vice president, she joined the advisory board of the Republican Unity Coalition, a group that sought to make the party more tolerant toward gays and lesbians. "We can make sexual orientation a nonissue for the Republican Party, and we can help achieve equality for all gay and lesbian Americans," she said in a 2002 statement. She later left the organization.
In the current campaign, the younger of the Cheneys' two daughters has served as director of vice presidential operations. She has been described as one of her father's closest political confidants.
Still, the Denver-area resident and her longtime partner, Heather Poe, have tried to maintain a low public profile. The older Cheney daughter, Elizabeth, took to the stage along with her four children after the vice president's speech at the Republican National Convention. Mary Cheney, 35, and Poe applauded from their seats.
White House spokesman Dan Bartlett said Kerry should have known his remark was "out of bounds." He added: "I think the public expects to have a vigorous debate on the issues, but leave the families out of it."
Relatives of national candidates, in the past, have not been immune from the political debate. Nancy Reagan's extravagant White House style, including her taste for fine china and clothes, became an issue. Kerry's wife, Teresa Heinz Kerry, has been taunted by some as a rich, out-of-touch patrician -- although Bush and Cheney have kept their distance from such critiques.
"Normally your family's safe -- they're protected. Every once in a while, [criticism] will extend to a first lady or a spouse," said Craig Smith, director of the Center for First Amendment Studies at Cal State Long Beach and a former GOP speechwriter. "That's where they draw the line. Going after kids is a totally different thing."
Ellen Andersen, an assistant professor of political science at Indiana University-Purdue University, agreed that family members were generally off-limits.
"In this case, though, we're talking about someone who's a full-grown adult who is active in the campaign and is openly gay," said Andersen.
"This [controversy] is predicated on the fact that there are a number of Americans that think homosexuality is shameful."
Leaders of several gay rights organizations commended Kerry for his comments.
"We saw John Kerry put a human face on what it means for someone to be gay," said Jacques of the 600,000-member Human Rights Campaign. "I believe he did so with great sensitivity and humanity in talking about gay Americans having the same rights, responsibilities and protections as every other American."
The dissent over Kerry's mention of Mary Cheney obscured what ultimately might be a more provocative statement: his position that sexual orientation is a given at birth.
While that contention is a matter of considerable research and remains unsettled, the near consensus in the scientific community is that sexuality "is not a matter of voluntary choice," said Fred Berlin, associate professor of clinical psychiatry and an expert on human sexuality at the Johns Hopkins University School of Medicine.
"You don't decide that; you ... discover that," he said.
Berlin said the vast weight of evidence pointed away from sexual identity being based on conscious choice.
"Even if it is early life experience, which is nurture," Berlin said, "it's still not a matter of a little child weighing their options and then deciding."
Times staff writers Michael Finnegan and Mark Z. Barabak contributed to this report.