Just a few days into her nascent campaign for Hillsborough County commissioner, Democrat Mariella Smith has picked up an endorsement from one of Tampa's best-known elected officials: U.S. Rep. Kathy Castor.Smith, running for the District 5 seat in a crowded primary field, announced the endorsement from the former commissioner-turned-Congresswoman on Tuesday."Mariella Smith is a champion for citizens, our neighborhoods, a healthy environment and a strong local economy. She has a deep understanding of how to move Hillsborough County forward on transportation, smart growth, the environment, and economic prosperity," Castor said in a statement. " She is a vigilant advocate for open and honest government and an outspoken partner on issues important to Hillsborough families. I have seen firsthand how she is not afraid to stand up to powerful special interests."Smith is a long-time activist and first-time candidate. Four other Democrats have announced plans to run in District 5: Mark Nash, Jamela Passmore, Elvis Jamine Piggott and Corey L Reynolds. Of that bunch, Nash and Piggott have had the most active campaigns and raised the most money.On the Republican side, County Commissioner Victor Crist is hoping to extend his time on the board by jumping from his north county District 2 to the countywide District 5 seat. Two Republicans have indicated plans to run, but have so far raised little money: Timothy Lynn Curtis and Angel Urbina Capo.