With the selection of Sen. Joe Biden as his vice presidential pick, Barack Obama has followed a tradition of more than six decades — Democratic presidential candidates choosing a member of Congress as their running mate.

Since Franklin Delano Roosevelt tapped the haberdasher-turned-senator from Kansas City, Harry S. Truman, as his vice president in his bid for a fourth term, every donkey veep pick — insert asterisk here — has been a U.S. senator or, less likely, a U.S. representative.

That roll call has included such luminaries as Kentucky's Alben Barkley in 1948, Alabama's John Sparkman in 1952 and Walter Mondale in 1976 and again in 1980. The only candidate who wasn't a senator was Geraldine Ferraro, a member of Congress from New York's 9th District when Mondale — by now his party's presidential candidate — selected her.

The asterisk? That was in 1972, when George McGovern tapped Thomas Eagleton, a senator from Missouri, as his running mate. Eagleton was dumped after his history of electroshock therapy became an uncomfortable issue, and he was replaced with Sargent Shriver, a member of the Kennedy family who had never held elective office.

The last "pure" non-legislative democratic vice presidential candidate was from FDR's third term, when he picked his own secretary of agriculture, Henry Wallace.

On the other side of the aisle, Republicans have been more diverse in their selections. As recently as 1968, Richard Nixon picked the former governor of Maryland, one Spiro T. Agnew, as his running mate. Agnew was again on the ticket for Nixon's re-election in 1972.

The elephants have also been less focused on the Senate in recent decades. Veep selections George H.W. Bush (1980 and 1984), Jack Kemp (1996) and Dick Cheney (2000 and 2004) all hailed from the House, although their respective résumés included other high-profile work for the executive branch.

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