While a weaker currency helps Chinese exporters, it also adds to the country’s already widening trade surplus with the United States.

A continued drop in the currency could start trade issues in the midst of the American presidential elections. Candidates mentioned China nearly two dozen times in Tuesday’s Republican presidential debate, none of them favorably. Carly Fiorina described China as a “rising adversary” and asserted that like North Korea, “they, too, recognize one thing: strength and their own economic interest.”

Some longtime American critics of China’s currency policies had tried to persuade the Obama administration to try to block the I.M.F. decision, contending that the renminbi continues to be heavily controlled by the Chinese government. Those critics of China’s currency policies point to the recent weakness as evidence.

“It’s not at all surprising to me that once they got what they wanted, the renminbi is sliding further downhill,” said Senator Chuck Schumer, Democrat of New York. “We have to take much tougher action against the Chinese government if we’re going to have success combating currency manipulation.”

The I.M.F. has a policy of not commenting on short-term currency fluctuations, while the People’s Bank of China and the United States Treasury very seldom do so. All three declined to issue statements on the renminbi’s drop since the I.M.F. decision three weeks ago.

The I.M.F. had said that China has adopted substantial reforms aimed at making the renminbi more “freely usable.” The Treasury accepted this in lending American support to the decision by the I.M.F.’s board to accept the renminbi. The I.M.F. and the Treasury have both urged China to let markets play a greater role in setting the value of the renminbi, which makes it harder for them to object now when market forces push down the currency.