In Congress, Harman is known as a hawkish Blue Dog. The Almanac of American Politics (sub. req'd) describes her record as "the most conservative of Democrats from Los Angeles." She was challenged from the left in recent elections by the progressive Marcy Winograd, who criticized Harman over her support for the Iraq war and general backing of post-9/11 surveillance and security methods put in place by the Bush administration.
In 2009, Harman weathered a scandal when she was accused of promising the American Israeli Political Action Committee that she'd work on their behalf if AIPAC would lobby then-Speaker Nancy Pelosi to make her the chair of the House Intelligence Committee. Harman denied the allegations.
A special election will have to be called this year to fill the remainder of Harman's current term, which of course began just over a month ago when the 112th Congress was sworn in. The 36th District she represents is rated solidly Democratic by most analysts.
Note: This post has been updated since it was first published.