BEIJING — Throughout his presidential campaign, Donald J. Trump has claimed that China is stealing American manufacturing jobs.

In a speech to the Republican National Convention on Thursday, Mr. Trump — the party’s nominee for the presidency — said that “disastrous trade deals” had hurt manufacturing jobs in the United States. Mr. Trump also argued that American support for China’s embrace of free trade had been a “colossal” mistake.

At one point, Mr. Trump’s argument had merit. With its large pool of workers who earned much lower wages than their American counterparts, China attracted manufacturers seeking to reduce costs, bolster profitability and keep prices low. Between 1999 and 2011, the United States lost at least two million jobs because of a surge in Chinese imports, according to a study published in The Journal of Labor Economics.

In today’s China, however, workers face a more troubled outlook than Mr. Trump suggests. They are losing their jobs because of a slowing domestic economy, rising costs and stiffer foreign competition — including from the United States.