Browse down the list of America's presidents, and you're bound to begin seeing double — only 38 of the 43 last names are different.

In the age of the Bush dynasty, Americans are no strangers to presidential legacies. But while the first pair of commanders-in-chief to share names — John and John Quincy Adams — mirror the father-son relationship we see today — George and George Walker Bush — linking the duos in between is less straightforward.

Benjamin Harrison was the grandson of cider-drinking William Henry, and the two Roosevelts, Theodore and Franklin Delano, were fifth cousins.

Most interesting of all is the pair who share a name, but not blood — Andrew and Lyndon B. Johnson. Both ascended to the presidency on the heels of nation-wrenching assassinations — Andrew followed Abraham Lincoln, and Lyndon John F. Kennedy —and both served rather unpopular terms exactly 100 years apart — Andrew, 1865-69, dealt with the aftermath of the Civil War, and Lyndon, re-elected 1965-1969, escalated the conflict in Vietnam and suffered the slings and arrows of resurrecting a legacy of the Civil War, civil rights.

The unsung hero in all this, however, has to be the missing link, John Scott Harrison. With both a father and a son as president (and a grandfather who signed the Declaration of Independence), he somehow missed the boat — and ended up a congressman from Ohio.

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This post is one of a Miller-McCune.com series on intriguing, amusing, and memorable moments of the American presidency inspired by the American Presidency Project (www.americanpresidency.org) and running until the November election.