The question is bound to come up again as her campaign spreads across the United States.

In response, some women are asking: Would a male candidate be asked to defend his likability? What does likability signify in a candidate, anyway? And can a female candidate even afford to be likable, without compromising the need to appear tough and competent?

As for Mrs Clinton herself, she tried to blunt the question with a little rueful humour before launching into her own defence.

'Well, that hurts my feelings,' she said. 'But I'll try to go on.'

It was an approach that impressed Daniela Ioan, a mother of two. In fact it was the debate, during which she felt Mr Barack Obama and Mr John Edwards were teaming up harshly on Mrs Clinton, that made Ms Ioan decide to support her.

'She's not measured by the same yardstick,' says Ms Ioan. 'Even if you don't like her, she shouldn't be scrutinized the way she is. I felt like I had to do something to help her.'

The likability question also rankles Ms Kate White, editor in chief of Cosmopolitan magazine. 'I think (it's) totally unfair,' Ms White says. 'She's brilliant, hardworking, energetic, clearly a great mother because she raised a dazzling daughter, and by the accounts of many people who know her, funny and warm. I don't see what's not to like.'

It is all emblematic of a long-standing double bind for female candidates, says one specialist in political communication.

'It's gender bias, plain and simple,' says Ms Kathleen Hall Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania.

'They're supposed to be warm and accessible, because that's what's perceived to be gender-appropriate. But they also need to be tough and competent. The minute they appear that way, their warmth and accessibility are called into question.' -- AP