About a year ago, I came across an article of political dynasties in US politics. The Bushes came in at #7. The Clintons didn't make the list (the requirement for being considered a dynasty was three generations). The top 10, in descending order, were Kennedy, Roosevelt, Rockefeller, Harrison, Frelinghuysen, Adams, Bush, Breckingridge, Taft, Bayard.
There is a level of endogamy in american politics which is spectacular, even by european standards.