(CNN) – U.S. Rep. Bob Filner stepped down Monday to become San Diego's mayor, though his seat in Congress – representing California's 51st Congressional district – will only remain vacant until the next Congress begins in January.
Filner, a Democrat, won his mayoral election on November 6 after serving ten terms in Congress. He'll be succeeded in January by Democrat Juan Vargas, a former state lawmaker who beat Republican Michael Crimmins by forty percentage points on Election Day. The 51st district covers California's entire border with Mexico, including the southeast corner of San Diego.
Filner's resignation means Democrats will have one less vote in the House during the lame duck session of Congress, when votes could arise on a deal to avoid the end-of-the-year fiscal cliff.