What are the three advantages of incumbency?

Three advantages of incumbency are 1. The presidents are already known in the political spectrum 2. They have rather no trouble running and funding their campaigns and 3. They have safe seats due to their experience and sometimes district advantage due to their parties control over a certain area that favors their political party.

Some of the advantages an incumbent may have are franking privilege, staffers, patronage, name recognition, casework, and money (especially from PAC's).