Johnston served as a Lodi Unified School District Board Member from 1979 to 1992. Several years later, in 1994, Johnston ran for the Stockton City Council and won. She successfully ran for re-election in 1998 and left the office in 2002. Years later, Johnston declared her candidacy for the city's mayor in
the 2008 election, and won, receiving 55.8% of the vote. On June 28, 2012, during her tenure as mayor, the City of Stockton filed for
Chapter 9 bankruptcy protection, making it the largest city in U.S. history to file for bankruptcy, until Detroit
filed for bankruptcy the next year. ==Electoral history==