Gary Clyde Hufbauer and Sean Lowry at the Peterson Institute for International Economics calculated the additional cost to consumers at $1.1 billion — or about $900,000 per tire job saved. But the wages of workers whose jobs were saved amounted to about 5 percent of that.

The lesson is not that protectionism is porous. It is. And it can be gamed. Until a few years ago, Ford attached rear seats and rear windows to the Transit Connect vans it imported from its plant in Turkey. Once they had gone through customs — paying the 2.5 percent tariff on passenger vehicles instead of the heftier 25 percent levied on commercial vans — the seats and windows were ripped out and recycled.

The critical takeaway is that the distortions brought about by trade barriers impose a cost on the economy. It might not be easy to spot before the fact, but it tends to be more substantial than whatever fleeting gains protectionism can bring about to the protected.

Think of the multifiber agreement, which until its demise at the end of 2004 allowed the United States to impose individual quotas on thousands of pieces of apparel — cotton diapers from China, trousers from Guatemala. The rationale was to protect one of the lowest-wage industries in the country from lower wages in the developing world. A study by the United States International Trade Commission cited by the Dartmouth economist Douglas A. Irwin in his 2002 book, “Free Trade Under Fire,” concluded that it had raised apparel prices by 18 to 24 percent, imposing a particular burden on poor households.

Sometimes the cost can squelch an industry. A 63 percent tariff on advanced flat-panel screens for laptop computers in 1991 helped drive a stake through the heart of the American laptop industry itself. Japan’s Toshiba stopped making laptops in the United States. Apple moved production to Ireland. An IBM spokesman called the decision “an eviction notice from the U.S. government to the fastest-growing part of the U.S. computer industry.”

Similarly, the ring of protection around the sugar industry almost killed it instead. Hoping to protect a price floor for sugar of 16.75 cents a pound even as world prices sank, in the 1980s Washington resorted to increasingly stringent import quotas that drove domestic sugar prices up to five times the world average.

Clever Canadian firms sent sugary cake mixes to the United States — where the sugar was extracted. Other countries grabbed on to the tactic. In 1985, Washington put emergency quotas on all imports of sweetened cocoa, cake mixes and edible preparations. South Korean noodles — with 0.002 percent sugar content — were snagged in the dragnet. So was kosher pizza from Israel.