Richard Bush, director of the Center for Northeast Asian Policy Studies at the Brookings Institution, said Romney will back off from the campaign pledge if he is elected.

Sun Zhe, director of the center for US-China relations at Tsinghua University, said Romney had taken "an extreme stance" toward China in the debate, which was "irresponsible" and would not work in practice, but might gain some votes.

"Neither Obama nor Romney will fulfill their campaign promises (on China) once elected, or there would be a trade war that would hurt both sides," said Guo Xiangang, a researcher into US studies at the China Institute of International Studies.

Negative campaigning

The showdown over who will be tougher on China mirrors countless campaign ads aired across the US during the last six months, especially in swing states such as Ohio, North Carolina and Florida.

China was the focus of 10 district ads from both Obama and Romney, according to the Campaign Media Analysis Group at Kantar Media. The ads ran 47,190 times over a 30-day period, ending Oct 8.

The seven Romney ads that mentioned China were broadcast 29,317 times, while Obama's three ads on China were broadcast 17,873 times. In them, Romney was accused of funneling US jobs to China through Bain Capital, the private-equity outfit that he co-founded in 1984.

Romney's ads repeatedly referred to China as a cheat. In one, called "Stand up to China," it was alleged that, "China is stealing American ideas and technology. Seven times Obama could have taken action, seven times he said no. His policies cost us 2 million jobs."

The belligerent campaign rhetoric has caused concern among some observers of US-China relations, regarded by many as the most important bilateral relationship of the 21st century.

"We must ask our leaders to abandon the campaign rhetoric and focus instead on a future of shared prosperity and cooperation," said Steve Orlins, president of the National Committee on United States-China Relations, at the committee's annual gala on Oct 8.

Henry Kissinger, a former secretary of state, who endorsed Romney, said on Oct 3 that he was "bothered" that both campaigns are "appealing to those suspicious of China" in order to win votes. The architect of modern Sino-US relations also criticized the candidates for using "extremely deplorable" language in describing China as a cheat.

"The sort of China-bashing in the presidential contest may be the strongest since the two countries began to restore ties in 1972. One reason is that China's greater economic clout stands out even more during the longest American downturn since the Great Depression," according to an editorial in the Christian Science Monitor.

Sun said frictions between the two countries, including the exchange rate issue and the protection of intellectual property, have increased as economic ties grow closer and more intertwined.

"These problems can only be resolved through dialogue and negotiation," he said.

China has actually helped to sustain political stability in the US, said Sun, adding that inexpensive Chinese exports have benefited the poor in the US.