Bill Clinton has become a symbol for both Hillary and Obama — and a vehicle each uses to throw an implicit negative at the other.
To Hillary, Bill demonstrates her experience and permits her to claim his record as president as her own. Without those White House years, her resume scarcely justifies her candidacy. But with it, she can picture Obama as an ingÃ©nue, incapable of “hitting the ground running” as president.
To Obama, Bill is a symbol of the past and of the mind-deadening alternation of the Clintons and the Bushes in power that will probably go down in history as one of the more brain-dead times in our politics (probably akin to the elections of 1884-1892 when Grover Cleveland flitted in and out of power, alternating with ‘Benjamin Harrison).
Each uses Bill as his or her own symbol in the classic match up of experience vs. change. (Usually, in times that are perceived as negative, change wins. But in times of war, experience wins).