No recent presidents can boast paternity that seems ordinary or normal, finding middle ground between the intense expectations of a powerful, prominent parent and the disasters of badly broken families with absent birth fathers.

In one sense, these extreme backgrounds now dominate the presidential process because that process itself has become so extreme. A rising politico can no longer wait for colleagues to push or pull him toward a White House race, or dream of sudden success at some brokered convention. A serious candidacy currently requires obsessive pursuit of power over the course of several years, with expenditure of tens of millions in campaign cash.

What sort of person willingly undergoes such an ordeal? More and more, it seems, either a privileged individual with a profound sense of entitlement, or an unlikely upstart whose status as miraculous survivor amounts to his own anointing. But despite a shared sense of determination and destiny, famous-father candidates tend to run dramatically different campaigns than do their no-father counterparts.

Sons of famous fathers work tirelessly to burnish family traditions and complete the unfinished business of prior generations. George W. Bush focused on winning the second term cruelly denied to his father, and Mitt Romney still hopes to claim the Republican nomination that his father lost to Richard Nixon in 1968.