Question:
Which political party did Pier Luigi Bersani belong to in Jun, 2004?

Context:
 Pier Luigi Bersani is a member of the Democratic Party from Oct, 2007 to Dec, 2022. 
 Pier Luigi Bersani is a member of the Democratic Party of the Left from Feb, 1991 to Feb, 1998. 
 Pier Luigi Bersani is a member of the Democrats of the Left from Feb, 1998 to Oct, 2007. 
 Pier Luigi Bersani is a member of the Italian Communist Party from Jan, 1960 to Feb, 1991.

Answer:
Democrats of the Left