The mayor shall be elected for a term of four years, commencing on the first day of January following the election, shall have been for at least one year immediately prior to the date of taking office both a resident of the city and a registered voter of the city, and shall continue as both a resident and registered voter of the city during the term of office. Except in the case of vacancies, the mayor shall be elected in the regular municipal election held in the year immediately prior to the year in which a presidential general election is held.