Why would you need to call TO_DATE on a column that is already in DATE format?
Edit: Does that even work at all?
Looking at the Oracle Docs for TO_DATE the usage model is
which shows the first parameter as 'char'. The text goes on to clarify that 'char' means "CHAR, VARCHAR2, NCHAR, or NVARCHAR2". So I doubt that a first parameter of DATE will be valid. (Disclaimer: I haven't actually tried it so I'd like to see arkaes or the OP try out these suggestions and report back)