Why would citing "a well-known historical source" be any different from citing a not-particularly-well-known historical source?
For the speech: you found the speech somewhere, right? Book, website, magazine? Cite that source.
For the U.S. Constitution, a quick Google of "rules for citing US constitution in bibliography" turns up this link from the APA Style Blog.
All citations of the U.S. Constitution begin with U.S. Const., followed by the article, amendment, section, and/or clause numbers as relevant. The terms article, amendment, section, and clause are always abbreviated art., amend., §, and cl., respectively. Preamble is abbreviated pmbl. (as in my opening quotation). Article and amendment numbers are given in Roman numerals (I, II, III); section and clause numbers are given in Arabic numerals (1, 2, 3). The Bluebook states that for parts of the Constitution currently in force, do not include a date. If you are referring to a part of the Constitution that has been repealed or amended, include the year that the part in question was repealed or amended in parentheses.