US Democratic presidential candidate Barack Obama has turned to humour in an effort to boost his campaign against rival Hillary Clinton.
Mr Obama has said he has trouble managing paperwork
Polls suggest the two candidates are neck and neck, ahead of a key race in Nevada on Saturday.
Republicans focused on the economy ahead of the primary in South Carolina, which is losing manufacturing jobs.
Candidate Mike Huckabee has been under fire for remarks apparently equating same-sex marriage with bestiality.
"Marriage has ... as long as there's been human history, meant a man and a woman in a relationship for life. Once we change that definition, then where does it go from there?" he said in an interview for Beliefnet online magazine.
"I think the radical view is to say that we're going to change the definition of marriage so that it can mean two men, two women, a man and three women, a man and a child, a man and animal."
David Smith of the gay rights Human Rights Campaign told CNN that Mr Huckabee, a former evangelist preacher, was "out of the mainstream of American thought".
In a speech to voters in Nevada, Mr Obama attacked Mrs Clinton for comments made in a TV debate on Tuesday.
The candidates were asked to say what their biggest weaknesses were.
Mrs Clinton has promised a "green collar" jobs programme
Mr Obama said he had a messy desk and found it difficult to manage paperwork, while Mrs Clinton said she was impatient to change America.
The Illinois senator sought to portray his rival as someone who could not give a straight answer.
"Because I'm an ordinary person, I thought that they meant, 'What's your biggest weakness?'" he said. "If I had gone last I would have known what the game was.
"And then I could have said, 'Well, ya know, I like to help old ladies across the street. Sometimes they don't want to be helped. It's terrible.'"
Meanwhile Mrs Clinton, campaigning in mainly black areas in California, promised to improve conditions for black voters.
She promised a "green collar" jobs programme, focusing on alternative energy sources, and a $200m programme to help ex-offenders coming out of prison.
Republicans are campaigning for Saturday's South Carolina primary. Democrats vote there a week later.
John McCain, who won New Hampshire, leads narrowly in the southern state.
But correspondents say he has failed to win over religious conservatives, most of whom seem to be backing Mr Huckabee.