Recently, President Obama was awarded an honorary doctorate from Notre Dame University. This type of unearned degree is given out frequently to American Presidents during and after their term in office. It is an honor that almost all doctoral granting institutions use as a way to attract commencement speakers and reward long-term donors.
However, only one American President has an earned doctorate. That is Woodrow Wilson. He received a Ph.D. from The John Hopkins University in 1886. He even had to write a dissertation. It was 333 pages long and titled Congressional Government: A Study in American Politics. This dissertation is readily available today from a variety of publishers.
Here is a description of the book:
Wilson divides Congressional Government into six parts. In part one, his introductory statement, Wilson analyzes the need for a federal Constitution and asks whether or not it is still a document that should be unquestioningly venerated. In part two, Wilson describes the make-up and functions of the House of Representatives in painstaking detail. Part three is concerned with taxation and financial administration by the government and its resulting economic repercussions. Part four is an explanation of the Senate's role in the legislative process. The electoral system and responsibilities of the president are the central concerns of part five. And Wilson concludes, in part six, with a both philosophical and practical summarization of the congressional form of the United States government, in which he also compares it to European modes of state governance.