Rep. Diane Watson (D-Calif.) is set to announce her retirement, according to Democratic sources.
Watson's central Los Angeles district isn't expected to be competitive in the general election, as it carries a distinct Democratic advantage as a majority-minority district. President Barack Obama won it 87-12 in 2008.
Former California State Assembly Speaker Karen Bass is thought to be an early front-runner to replace Watson.
Watson, 76, has served in Congress since 2001. Prior to that, President Bill Clinton appointed her ambassador to Micronesia.