Here is a web page with audio clips of Lyndon Johnson discussing numerous issues during the 1964 campaign.
http://allthewaywithlbj.com/
For more audio recordings of Presidents such as the following:
Franklin D. Roosevelt
Harry S. Truman
Dwight D. Eisenhower
John F. Kennedy
Lyndon B. Johnson
Richard M. Nixon
Go to the Miller Center, University of Virginia to listen to those. Transcripts available there as well.
http://millercenter.org/academic/presidentialrecordings
