In recent weeks, the presidential candidates have been tussling over a familiar campaign issue in postindustrial America: how to reinvigorate manufacturing.

Former President Donald J. Trump has proposed stiff tariffs on nearly all imports as a way of forcing foreign companies to make their goods in the United States, an escalation of a strategy that did not work during his term. “We’re going to take their factories,” Mr. Trump declared recently.

Building on the Biden administration’s approach, Vice President Kamala Harris has promised tax credits and more apprenticeships to strengthen factory towns and invest in advanced technologies, ensuring they “are not just invented in America but built here.”

In truth, no president can single-handedly control the growth of specific industries. Larger economic forces like recessions and exchange rates tend to play a much more powerful role. But some policies can help or hinder their progress.

Over the last four years, policy and macroeconomic factors have combined to begin reshaping the manufacturing industry. While job growth has been flat for the past two years — as interest rates have clamped down on expansion and a strong dollar has dulled exports — shifts in the composition and location of it are underway beneath the surface.

But first, a more fundamental question: Why do politicians care so much about manufacturing, anyway?