How can you verify a presidential connection? What is available to you to help in your search? When researching a famous connection, remember that it is not enough to have the same surname or to have a story in the family. Just like a childhood game of "telephone," family stories become embellished over time and may come out relating you to someone famous when the original story was quite different. Sometimes, and I hate to say this, our ancestors stretched the truth a little bit. They may have proclaimed they were related to a President for various reasons, that doesn't make them 'bad', it just means that they had some motivation for proclaiming it.
When taking on a project where you are researching your connection to a famous person you want to take it in two steps. First, research your family history and then, second, research the ancestry and descendants of the famous person. This can aid you in checking out whether the two match up at all. When I have researched clients' connections to famous people, this is what I have done. It helps you to determine whether there is a possible connection and whether the family story checks out. In one case, by researching the ancestry and descendants of a historical figure that a client was sure he was related to, I could tell very quickly that the historical figure's family was from a different part of the county and that other facts did not match for a link to the client's family.
Online and in book form, there are many resources for checking out the ancestors and descendants of people in the Presidency. Kimberly Powell at About.com, http://genealogy.about.com/od/presidents/a/genealogies_2.htm, has an online article about tracing the ancestry of Presidents with links to comprehensive information about each president and his spouse.
There are several individuals and groups who have worked hard to provide pedigree charts and family histories of Presidents online. The Dynamic Family Tree, http://history.fulton.missouri.org/Presidents/USPresidents.html, is a graphic, interactive website that shows pedigree charts and biographical information. The website is also available in numerous languages. Genealogy of the U.S. Presidents available at http://www3.dcs.hull.ac.uk/genealogy/presidents/, provides some biographical information as well as information on the spouse and children. My warning about these two websites is that they do not contain sources, so with all undocumented work, use this only as a jumping off point, but then verify it with primary documents.
Genealogy.com has a section of its website dedicated to the family trees of famous people. At http://www.genealogy.com/famousfolks/ you can check out not only celebrities and historical figures but also politicians. The search engine just requires that you type in the name of the famous person and then it takes you to a page where you can read a little biographical data and then connect to a family tree.
Don't forget, that by using a search engine like Google, and typing out a search term like "Richard Nixon family tree" you will also find websites that contain genealogical and biographical information.
For information about political burial spots, try searching The Political Graveyard at http://politicalgraveyard.com/. From the famous to the obscure politician, this website provides information on the grave sites of those in politics. With over 180,000 politicians, judges and diplomats, you can search by name, locality, year of birth or death or offices held.
Some books that might assist your search include, A Genealogy of the Wives of the American Presidents and their First Two Generations of Descent> by Craig Hart (ISBN 978-0786419562); The Descendents of the Presidents of the United States of America by Walter Lewis Zorn; and Ancestors of American Presidents: First Authoritative Edition by Gary Boyd Roberts (ISBN 978-0936124193). For more information about U.S. Presidents, don't forget to look at the Family History Library catalog at www.familysearch.org. Conduct a keyword search on the word "Presidents" or the name of the president you are most interested in and you will be provided a list of available materials from the Library that you can then access at a Family History Center.