Gov. John Carney of Delaware is about to do something that no other governor in modern American history has done — step down as a state’s leader and immediately take office as a mayor.

In his campaign for mayor of Wilmington, a city of 71,000, he and his staff knocked on more than 11,000 doors and have been met, at times, with confusion by voters.

“The main thing they would say is, ‘Isn’t this a step down?’ And I would say, ‘Well, I don’t think so,’” Mr. Carney said.

“It is arguably on a given day a harder job,” he added. “In that sense, it’s a step up.”

Term limits prevented Mr. Carney from running again for governor, and he has already had most other jobs in Delaware politics, having served as lieutenant governor and as the state’s lone representative to the U.S. House.

Governor Carney won the Democratic primary for mayor in September, and is without a Republican opponent in next week’s election, putting him on the precipice of making history. He even plans to vacate the governor’s office a few days early to be sworn in as mayor. (Other governors have later served as mayors — Jerry Brown in California, for example — but there has always been an interlude between the holding of the two offices.)

Mr. Carney, 68, spoke to The New York Times about his decision, and why the possibility of running for a U.S. Senate seat did not appeal to him. This interview has been condensed and lightly edited for clarity.

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