Democratic presidential candidate Pete Buttigieg’s former chief of staff won an election Tuesday to succeed him as mayor of South Bend, Ind.

James Mueller, a Democrat who was a high school classmate of Buttigieg and later became his top staffer as mayor, defeated Republican Sean Haas in the contest, according to local news reports.

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“Big congratulations to James @MuellerforMayor and all of the South Bend Common Council members elected tonight!” Buttigieg tweeted. “Great opportunities are ahead for continued progress and inclusive growth in our hometown.”

Buttigieg, as he prepared to enter the Democratic presidential primary, announced last year that he would not seek a third term as mayor.

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Buttigieg endorsed Mueller in the race, and his campaign had tweeted a photo of him voting earlier Tuesday.

The South Bend Tribune reported that the race was seen as a referendum on Buttigieg. Republicans have not won the seat since 1967.