Democratic presidential candidates fired a stinging round of attacks at China on Tuesday, bemoaning "bad food" imports and defective toys while accusing Beijing of manipulating the yuan.
It was the first sign of "China bashing" -- a staple of past US campaigns -- and came as candidates debated before 15,000 labor-union members concerned about lost US blue-collar jobs and the impact of global free trade.
Front-runner Senator Hillary Clinton said that the US had to deal with China's "currency manipulation" at the forum hosted by the AFL-CIO trade unions federation.
"We have to have tougher standards on what they import into this country," she said.
"I don't want to eat bad food from China or have my children having toys that are going to get them sick," said Clinton, who according to a new USA Today/Gallup poll leads the Democratic field by 22 points.
Her comments referred to a string of recent consumer health safety scares in the US involving goods made in China.
The outdoor debate on a humid night at a football stadium was seen as an audition before the mighty labor block, which partially bankrolls and gets out the vote in Democratic campaigns.
Senator Barack Obama, second to Clinton in national polls five-and-a-half months before first party nominating contests, branded China a "competitor" but not necessarily an enemy.
"If they're manipulating their currency ... we take them to the mat," he said.
New Mexico Governor Bill Richardson, a long-shot candidate with experience in foreign relations, warned that China was a "strategic competitor."
"We've got to say to China, `you've got to stop fooling around with currency; you've got to find ways to be more sensitive to your workers,'" he said. "And we've got to be tougher on China when it comes to human rights and trade ... You've got to do more, China, in the area of human rights around the world, like put pressure on the Sudan to stop the genocide in Darfur."
Former vice presidential candidate John Edwards also brought up concerns over defective Chinese imports, after US toys giant Fisher-Price recalled nearly 1 million Chinese-produced toys over fears they might be toxic.
"We should have a Consumer Product Safety Commission that's not looking out for big multinational corporations, but is actually looking out for the safety of our children here in America," he said.
Veteran Democratic Senator Joseph Biden lashed out at Chinese loans to the administration of US President George W. Bush which he said were used to fund the Iraq war.
"They hold the mortgage on our house ... We're now in debt almost US$1 trillion to China," he said.
Top contenders also sparred over whether to unilaterally strike al-Qaeda in Pakistan and battled on the influence of corporate lobbyists in US politics.
Obama rebuked rivals who mocked him as naive on foreign policy, defending his statement last week that he would be prepared to order unilateral strikes against al-Qaeda in tribal areas in Pakistan.
"I find it amusing that those who helped to authorize and engineer the biggest foreign policy disaster in our generation are now criticizing me," he said.
"If we have actionable intelligence on al-Qaeda operatives -- including [Osama] bin Laden -- and [Pakistani President Pervez] Musharraf cannot act, then we should. Now, I think that's just common sense," Obama said.