The mayoral and City Council candidates in an Iowa town who were most closely aligned with the message promoted by Americans for Prosperity, the deep-pocketed conservative political group, were roundly defeated on Tuesday in a sharp rebuke of outside influence in local politics.

The group, founded by the billionaire brothers Charles and David Koch, did not back specific candidates, but it targeted incumbents in the town, Coralville, for their role in running up a $280 million debt. Yet the involvement of an outside group provoked so much anger that the race became as much a referendum on the group’s involvement as on the issues themselves, and it captured national attention, including from the White House. Vice President Joseph R. Biden Jr. called the newly elected mayor, John A. Lundell, who was a City Council incumbent, on election night to congratulate him for overcoming the outside influence.

If anything, people in Coralville said, Americans for Prosperity’s efforts backfired and helped the candidates whose positions it was criticizing.

“The intrusion of the Americans for Prosperity pretty much poisoned the water of what we were trying to do for the last couple of years,” said Douglas Paul, a member of Citizens for Responsible Growth and Taxation, a group made up mostly of area business owners that also spoke out against the debt and the town’s economic development strategy.