It seems there are a variety of family ties in politics. Nancy Pelosi is the daughter of politician Thomas D’Alesandro II. Hillary Clinton is Bill Clinton’s wife. Dodd, Bush, Udall, Romney, Kennedy, etc. are all people who became politicians but who had family members before them who were already involved in politics.
So what percentage of national politicians are related to other national (or high state ranking) politicians within 2-3 generations (children, grandchildren, first or second cousins, spouses, etc) vs. the percentage who are more trailblazers and have not had anyone in their family enter major public office (president, representative, senator, mayor of a large city, governor)
People like Cheney and Obama seem to not be related to anyone who was already a politician. But GWB and Clinton were strongly tied to other existing politicians.