The poll is based on interviews conducted on February 8-11, 2015 with a random sample of 837 adults, aged 18 and older, living across the country.
A different kind of threat
"China is distinct from the other countries that typically rank among the top U.S. enemies in that it represents primarily an economic threat to the U.S., whereas Russia, Iran, Iraq and North Korea represent more of a security threat," said Gallup.
"International events over the past year, particularly the dispute with Russia over the Ukraine situation and the growing influence of ISIS militants in Iraq and Syria, have likely made countries other than China seem more threatening to the U.S," it said.
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A simultaneous strengthening of the U.S. economy and slowdown in China's economy is another possible factor in Americans' seeing the mainland as less of a threat than in recent years.
Last year, China's economy grew 7.4 percent, its slowest pace in 24 years, undershooting the government's target for the first time since 1998. Meantime, the U.S. economy expanded 2.4 percent, up from 2.2 percent in the year before.
"As Americans have grown more confident in the health of the U.S. economy, their views of what threatens the U.S. may shift more to security concerns than economic ones," Gallup said.
The proportion of Americans that regard "the economic power of China" as a critical threat to the vital interests of the U.S fell to 40 percent, down from 52 percent in both 2013 and 2014.