Yep it is hard to libel a public person. This goes back to some anti-civil rights for African-Americans suing the NAACP in the 1960s. The NAACP made some errors in a ad in the NY Times about some Southern office holders. They sued the NAACP for libel hoping to break the organization. The US Supreme Court came up with this public person exception for that case.
N.Y. Times v Sullivan.
Origin of the term "actual malice".