JEFF GREENFIELD:

It's exactly what's happening to Democrats in state after state. As with George W. Bush back in 2006, the president's unpopularity – he's barely above 40 percent nationally and well below that in key senate battlegrounds – is proving to be a very heavy burden.

In Alaska, Senator Mark Begich – son of a congressman – is being hammered by Dan Sullivan for his votes supporting President Obama. In Colorado, Senator Mark Udall – son of a congressman, nephew of an interior secretary – is trailing Cory Gardner in the polls. In Arkansas, Senator Mark Pryor – whose father was governor and senator – is struggling against Congressman Tom Cotton.

What links these campaigns is the same question: Can the family ties of these incumbents help define them as local champions, rather than as allies of an unpopular president? They also point to a striking fact about American political life. To a remarkable extent, it is and always has been a family business. It's not just these endangered Democratic incumbents.

Andrew Cuomo, cruising to a second term as New York's governor, is the son of a former governor. So is California's Jerry Brown, heading for a comfortable re-election 56 years after his dad Pat first won the job.

Shelley Moore Capito, the likely next Republican senator from West Virginia, is the daughter of ex-governor Arch Moore. Georgia's Michelle Nunn, daughter of ex-Senator Sam Nunn, is fighting for a senate seat against David Perdue, cousin of a former governor. While Jason Carter, grandson of the ex-president, is in a close race to be that state's next governor.

All told, at least three dozen members of Congress have had family members who've held political office before them.

This may seem at odds with one of America's founding ideas. The United States was born in part in rebellion against family privilege; our Constitution forbids titles of nobility, but in fact, America has had a class of political nobility almost from the beginning.

From the Adams, to the Harrisons, to the Roosevelts of New York, to the Tafts of Ohio, to the Longs of Louisiana, to the Kennedys of Massachusetts, to the Bushes of Connecticut, Texas and Florida. One generation of politicians seems to beget another. Maybe, says Moon Landrieu, it's simply like any other business.