Senator John Kerry's wife had to pull back on a tactless remark about Laura Bush, writes Conor O'Clery.
Teresa Heinz Kerry has developed a First Lady-like poise and modesty.
She no longer wears the expensive silk scarves that are popular with rich ladies, and now appears at rallies in tasteful trouser suits.
When her husband was speaking on the open-air stage at Carnegie Mellon University on Wednesday evening, she stood demurely to one side, hands clasped in front. The billionaire ketchup heiress had introduced Senator John Kerry with her usual directness.
"We are an optimistic people, a can-do people. We can get down and dirty and get things done," she said.
However, her directness can sometimes cause problems. Earlier she told USA Today that Laura Bush never had a "real job". After Republicans expressed outrage and Democrats dismay at her swipe at the popular First Lady, Mrs Heinz Kerry hastily issued a written apology, which was handed out to journalists at the rally in Pittsburgh.
"I had forgotten that Mrs Bush had worked as a schoolteacher and librarian, and there couldn't be a more important job than teaching our children," she said, and "I am sincerely sorry I had not remembered her important work in the past."
John Kerry kissed her on the forehead and got the crowd roaring by saying: "Pittsburgh is going to be the home of the next first lady."
This is one place in America where the Democratic candidate's wife is popular. The name Heinz is synonymous with the steel town, and her foundation has funded education and environmental projects in western Pennsylvania.
There have been rumours among Democrats about a character attack by Republicans on Mrs Heinz Kerry in the "down and dirty" last days of the election campaign.
Some conservative talk shows saw an opportunity to savage her in the remark about Laura Bush. The apology limited the damage, but the incident nevertheless left an image of a somewhat detached and haughty heiress.
The President's adviser, Karen Hughes, said the remark revealed "an unfortunate mindset" that sought to divide women between those who worked outside the home and those who worked at home. Senator Kerry, as if apologising for his wife, told the rally she was a "good soul" who "has gone through transformations" and who had helped change Pittsburgh for the better through her philanthropic work.
"What I love about her, and what America loves about her," he added defiantly, "is this is a woman who tells what's on her mind and tells the truth to the American people."
This brought cheers from the crowd of 35,000 that turned up for the rally, many more than expected. The couple were due to arrive at 6 p.m., but two hours before that a queue, mainly of students, stretched for a mile from the rally site, across the campus and down several blocks of Forbes Avenue.
The sight had Democrats sniffing victory. Mark Purcell, a long-time Democratic activist, said: "I think we are going to win because this is the most energised campaign to get the vote out I've seen in 35 years - and when the Democrats come out the Republicans can't beat them."
A Pittsburgh businessman, Sean McClorey, said the rally reminded him of the big crowds that turned out for Bill Clinton in the 1990s.
"This event is 'Clintonian'," he said, recalling that by comparison the Pittsburgh rallies for Al Gore in 2000 were "anaemic". Gore won Pennsylvania by five points in 2000, and the state is now the site of a ferocious battle.
George Bush followed Kerry yesterday with a campaign stop in Hershey, the Pennsylvania chocolate town, and Condoleezza Rice came to Pittsburgh yesterday to speak at the Hilton Hotel. It was not an official campaign stop - national security advisers are supposed to stay out of party politics - but Ms Rice has been making overtly partisan speeches in swing states.
Referring indirectly to Kerry, she said that for some the war had a limited objective - to go after bin Laden - but it was a "fundamental misunderstanding" to think the war on terrorism could be narrowed to Afghanistan.
In these frantic final days everyone who can rally the base is being called into action. Bill Clinton will be with Kerry on Monday in Philadelphia, and Arnold Schwarzenegger will campaign for Bush in Ohio next week.
The actor Ted Danson (Sam in Cheers) turned up at the Kerry rally in Pittsburgh to praise his record on the environment.
His father was a Republican, he said, "but he would be horrified with what this government has done to the environment".
The rock star Jon Bon Jovi came bouncing through screaming fans to the stage. "I hope you realise truth is on this side of the street," he said. "Young people, trust me, you have to vote to make a difference. This time the world is watching you."
As he sang Living On A Prayer and Bad Medicine, which Kerry later quipped summed up Bush's economic and health plans, Teresa Heinz Kerry for once seemed to be enjoying herself.
Yesterday, Laura Bush accepted Mrs Kerry's apology graciously, saying she knew what it was like when trick questions were asked.