On Tuesday, Barack Obama declared the debate over how to restore growth, balance, and fairness to the American economy the “defining issue of our time.”

“This is a make-or-break moment for the middle class,” he said in a Kansas speech, “and for all those who are fighting to get into the middle class.”

The following day, Republican front-runner New Gingrich said Mr. Obama “represents a hard left radicalism” and is “opposed to capitalism and everything that made America great.” The answer, he said, was slashing taxes and the size of the federal government.

The arrival of the middle class at the center of the American political debate is a step forward, but Obama and his conservative rivals steered clear of an ugly truth. Revitalizing the American middle class in a transformed global economy is a staggeringly complex task. And neither Democratic nor Republican orthodoxy alone is the answer.

A recent study by MIT professors Frank Levy and Thomas Kochan laid out the depth of the problem. Rising blue-collar employment after World War II allowed the United States to create what Obama called “the largest middle class and the strongest economy that the world has ever known.” Now that those factories have moved en mass overseas, the U. S. faces a far more arduous undertaking.