A worker lowers the body of a truck onto its chassis on the frame assembly line at the Toyota Motor Corp. manufacturing facility in San Antonio, in 2014. (T.J. Kirkpatrick/Bloomberg)

Commerce Secretary Wilbur Ross's Sept. 22 op-ed, "NAFTA's 'rules of origin' are killing American jobs," is a textbook example of the expression "can't see the forest for the trees." A focus on bilateral trade balances or content requirements obscures a much larger and more important picture.

In the case of the North American Free Trade Agreement, more than 1 million more vehicles were produced in the United States last year than in the year before NAFTA. Since NAFTA, U.S.-built auto exports have doubled and auto plants have been built in Texas, Tennessee, Georgia, Mississippi and South Carolina. Existing plants in Indiana, Kansas, Kentucky, Michigan, Missouri and Ohio have expanded, and more are planned.

Within the past month, Toyota and Mazda announced plans to build a U.S. assembly plant while BMW, Ford, Honda, Mercedes-Benz and Volvo Cars announced major expansions of their existing U.S. plants. In addition, GM has invested almost $3 billion in the past year and FCA US, the American subsidiary of Fiat Chrysler Automobiles, has made new U.S. investment commitments of more than $9.6 billion.

This is the more important story that needs to be told. NAFTA, by encouraging open trade and investment, has been key to keeping the U.S. auto industry competitive. The United States leads the world in innovation because it’s so open and competitive.

Mr. Ross’s proposed NAFTA rules-of-origin changes would jeopardize the U.S. auto industry and the 7 million jobs the sector supports.

The United States will get lost in the forest if we focus on trade balances or content rules.

John Bozzella, Washington

The writer is president and chief executive of the Association of Global Automakers.

Mitch Bainwol, Washington

The writer is president and chief executive of the Alliance of Automobile Manufacturers.