Five years ago, Mayor Michael A. Nutter proposed a tax on soda in Philadelphia, and the industry rose up to beat it back.

Soda lobbyists made campaign contributions to local politicians and staged rallies, with help from allies like the Teamsters union and local bottling companies. To burnish its image, the industry donated $10 million to the Children’s Hospital of Philadelphia.

It worked: The soda tax proposal never got out of a City Council committee.

It’s a familiar story. Soda taxes have also flopped in New York State and San Francisco. So far, only superliberal Berkeley, Calif., has succeeded in adopting such a measure over industry objections.

The obvious lesson from Philadelphia is that the soda industry is winning the policy battles over the future of its product. But the bigger picture is that soda companies are losing the war.

Even as anti-obesity campaigners like Mr. Nutter have failed to pass taxes, they have accomplished something larger. In the course of the fight, they have reminded people that soda is not a very healthy product. They have echoed similar messages coming from public health researchers and others — and fundamentally changed the way Americans think about soda.

Over the last 20 years, sales of full-calorie soda in the United States have plummeted by more than 25 percent. Soda consumption, which rocketed from the 1960s through 1990s, is now experiencing a serious and sustained decline.