Since 1964, Mellman notes, incumbents with approval ratings below 50 percent in the spring and summer of the year when they are running for reelection have always lost...By contrast, incumbents with approval ratings above 50 percent five and six months before the election always won...Bush's current approval rating is in the mid- to upper 40s.
Every incumbent who has won reelection in modern times had a double-digit lead over his opponent at this stage in the race, Mellman notes. A single-digit lead isn't enough. That's what the first Bush had over Clinton in early summer 1992. Carter held a small lead over Reagan in early summer 1980, and it survived until late October in many polls. Both those incumbents lost. So that puts Bush in company that he'd rather not keep.
"It's a pretty solid picture," he said. The problem for Bush is that a challenger enjoys natural advantages that tend always to erode an incumbent's early lead: "If a challenger runs an effective campaign, and that always has to be assumed, you've got to have a margin for the incumbent, because you almost always lose support as the challenger becomes better known, and is better able -- and I think this is often overlooked -- to pick and choose which issues can be driven to the disadvantage of the incumbent."