Bill Clinton's selection of Al Gore changed forever the calculus presidential candidates need to use in choosing their running mates. Previously, presidential candidates usually used their VP pick to help them to carry a pivotal state or region, as JFK did in choosing Lyndon Johnson in 1960.

But the single state theory doesn't work anymore. Voters can tell the difference between the first and second place on the ticket and don't let the tail wag the dog in determining their votes. After all, John Kerry couldn't carry North Carolina even after putting Edwards on his 2004 ticket.

Instead, presidential candidates should use their VP choice to make a statement about their own candidacy. The vice president is a candidate's first and most important appointment. Gore served Clinton well because his selection made the generational subtext of the race against Bush Sr. explicit — two babyboomers challenged the last of the G.I. Generation presidents.

This year, Barack Obama suffers from an obvious lack of Washington and national security experience. Even his most avid fans have to wonder if two years in the U.S. Senate (before he started to run for president) is enough experience. Just as Bush, who had never served in Washington, chose Cheney and Dukakis looked to Lloyd Bentsen to provide gravitas and federal expertise, so Obama needs to look toward Washington in finding his running mate.

He needs to select someone with national security credentials and DC know-how. Senate Foreign Affairs Committee Chairman Joe Biden (D-Del.) impressed us all in the Democratic debates. He, or Senator Chris Dodd (D-CT), would make good choices.

Obama would be ill-advised to choose Hillary since Bill comes as part of the package. The former president's lack of campaign trail discipline and questions about his recent financial dealings would dog the Democratic ticket, burdens Obama does not need.

The obvious temptation for Obama is to choose another woman to reach out to the Hillary supporters. But it's hard to find one who satisfies the need to bolster his national security credentials.

For McCain, the pressing need is to lend excitement to his candidacy. His low key delivery (one often wonders if he is putting himself to sleep with his own speeches) does not provoke anything like the excitement that Obama does. He needs to go for a "WOW" in his choice of a vice president — like Mondale did in 1984 when he chose Geraldine Ferraro. He lost, but it wasn't Gerry's fault. Continued...