Julian Sanchez identified this precise problem back in 2008 (and I'm sure he wasn't the first either).

Sanchez cites examples of Truman using an FBI wiretap on a potential supreme court nominee and Johnson wiretapping Martin Luther King and indirectly wiretapping presidential candidate Richard Nixon (ironic given how crazy Nixon went with wiretapping once he got into office).

http://articles.latimes.com/2008/mar/16/opinion/op-sanchez16