Harris resigned abruptly Thursday, two weeks after filing, after learning she was breaking one of the election laws she was elected to enforce.
"Well, it's another bizarre twist in the never-ending Katherine Harris saga," said state Democratic Chairman Bob Poe. "It's obvious she never understood the law. She couldn't even exit gracefully and resign properly."
Democrats are still upset with Harris for her role in the five-week dispute over presidential results in the Florida election two years ago. Republicans say she is a hero who is being mistreated.
As a result of the election recount dispute, President Bush won Florida's 25 electoral votes and the national election.
Republican Chairman Al Cardenas said voters "are so sick and tired of Katherine being attacked that whether this latest salvo is justified or not they just figure enough is enough. I think she's almost immune from criticism at this point because it's been so frequent and so strong against her."
All state officeholders are required to submit letters of resignation when they file to run for federal office, although they don't have to be effective until the after the elections.
Harris admitted to making a mistake and abruptly resigned as secretary of state. There are reports that Democrats would like to go to court to stop her from running for Congress, but legal experts say there is little chance that would be successful.
Harris is considered a shoo-in to win the vacant congressional seat in her hometown of Sarasota, Fla.
Gov. Bush appointed Jim Smith to replace Harris until Jan. 7 when the elective office of secretary of state will be abolished under a reorganization of the state's governmental structure. After that, the governor will appoint someone to carry out the secretary of state's election duties.
Smith served as Florida's secretary of state from 1987-1995 and attorney general from 1979-1987.