Are historical speeches public domain?
The text of speeches made and written down before 1923 are definitely in the public domain in the United States. This follows the general rule that any work published before 1923 is in the public domain. Any audio recordings of speeches made before 1923 are also certainly public domain, but audio or video recordings of historical speeches are subject to a much more complicated inquiry to judge whether or not they are public domain.
Speeches written and given by employees of the federal government (the President and Congressmen for example) are also in the public domain. This is because of the general rule that all works created by the federal government are in the public domain. The recordings of those speeches may or may not be in the public domain. If the recordings were made directly by the federal government, then the recording is certainly in the public domain, but if the recording was made by a person or company, only the text of the speech is in the public domain; that specific recording is protected by copyright.C-SPAN's video coverage of the floor proceedings of the U.S. House and Senate is in the public domain. Anyone can use the text of the speeches as well as the full recordings of those speeches that CSPAN makes.
From C-SPAN Classroom's"Copyright Policy for Educators"The video coverage of the floor proceedings of the U.S. House of Representatives and of the U.S. Senate is public domain material and is not subject to this license, and as such, may also be used for educational purposes."