Call me a cynic, but I think Zell Miller simply wants to avoid Max Cleland's fate by sweet-talking Republicans in GA (careerism, in other words).
Not the case. Zell Miller is the single most popular Georgia politician. Georgians, Republican and Democrat alike, love the guy and always have. He could have come out totally against Bush and Georgians, for the most part, would still love him (I even would, just for the good he's done for this state). With Cleland, he was only loved and respected by half of the state - the half that is Democratic. Miller is loved by everyone.
The fact that Miller, a Democrat, is endorsing Bush, a Republican, is HUGE in Georgia - maybe even huge in the entire South. It will influence those old southern Democrats who think the Democrats of today - Clinton's day - are still the Democrats of FDR's day - which they clearly are not.