The U.S. Constitution (Article 1, Section 8) protects the right of the creator of a work to its exclusive use:
The Congress shall have Power…To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries…
The Copyright Law of the United States of America gets revised periodically by different legislative acts that you might hear about in the news (Sonny Bono Act, TEACH, DMCA). All these revisions end up in the Copyright Law in the latest version of the United States Code.
CONFU was a serious attempt to determine what constitutes fair use that united 93 public and private copyright-owning and copyright-using entities to negotiate a consensus. The effort which took place in 1996 during the presidency of Bill Clinton, met little success because of conflicting interests. Read a summary: Building on Others’ Creative Expression (University of Texas Library).