In writing about trials and arrests, make sure you check the record. Before the person is found guilty, always use words like "alleged" or "accused." In America, everyone is considered innocent before proven guilty.
Associated Press Style and Libel Guide.
You are right, it is EXTREMELY difficult to find slander or libel on a public person, including politicians. Curious situation. Both sides have legal teams. Where's a lawyer when you need one--- to explain this! ;)
If Nixon was president in 1968 (which he wasn't) then Kerry is a liar - it's that simple!