NAFTA opponents point to the 2.4 million U.S. manufacturing jobs that have disappeared since NAFTA took effect in 1994, a drop of about 14%. In Ohio, site of Tuesday's hotly contested primary, manufacturing jobs are down by nearly 200,000, or 20%, during the same time.

NAFTA supporters — this page among them — usually respond by pointing out that 39 million jobs outside of manufacturing have been created in that time in the USA. Even Ohio has seen a net gain of 900,000 jobs, including 60,000 in finance, 80,000 in professional services and almost 190,000 in health care.

The reality is that NAFTA has relatively little to do with either the overall job losses or job gains. Communist China is a far larger factor. But the number that best displays the nonsensical nature of the debate is 66% — the increase in the manufacturing output of American industry since 1993.

It's impossible to look at an economy that has increased its manufacturing output so dramatically while simultaneously cutting its manufacturing workforce and not see a much larger force at work than NAFTA.

That force has been the unprecedented and sweeping gains in worker productivity that have allowed U.S. companies to churn out more goods with fewer people. Some of this has come from outsourcing the most labor-intensive parts of manufacturing, particularly to Asia. But much of it is from the use of more automated systems for assembly lines and high-tech inventory management.

Put another way, the main job killer of the past 14 years has not been the "giant sucking sound" of jobs going to Mexico, as enunciated by Ross Perot. Rather it has been that giant humming sound of machines replacing humans. Overall, this increased productivity has led to rising living standards and made the American economy more competitive. It has also left some people behind at a cost of considerable personal pain.

But to make NAFTA a centerpiece of the debate over the manufacturing economy is cheap pandering. Modifying or scrapping NAFTA wouldn't create jobs or more skilled workers. The idea raises false hope and seeks to scapegoat Mexico and Canada.

The only real answer to the problem of declining employment in manufacturing lies in educating younger workers and retraining older ones. This is, to be sure, a big challenge and a tough sell politically. American schools continue to under perform, particularly in technical knowledge. And most federal retraining programs have failed.

Any other answer, however, is simply not responsive to the problem — a workforce with too many people lacking the skills to prosper in a global economy and climb into the middle class. Fixing this is both essential for the economy and vital to U.S. democracy.

For these reasons, it would be nice to hear more from senators Clinton and Obama about creating a more educated workforce — and less about why they hate NAFTA. In 2004, before they were trying to win the Ohio primary, Clinton said "on balance NAFTA has been good" and Obama said the USA "benefits enormously from exports" under NAFTA.

They had it right the first time.