A couple of interesting things here
. In a highly polarized year, it does make sense to rest extra hope on mobilizing the base. But a polarized electorate might also suggest an electorate needing less hand-holding. It depends on whether the cores are excited about their candidate or really opposed to the alternative. People will get out to oppose someone they really despise, but they're more likely to turn out to support someone who excites them. The Bush decision is a gamble, especially because it isn't entirely clear that his base (social conservatives and hawks) will spill their support onto the rest of the party (fiscal conservatives and moderates).
The "center" may be smaller this year, but that doesn't necessarily mean that there are no swing votes to be won. Bush's challenge is to invigorate his base without alienating his right-leaners. Few on the Left ever believed Bush's "compassionate conservative" posturing, and his tenure of gay bashing, wealthy-tax-cutting, and child-behind-leaving, have proven us right. Still, there are people on the right who honestly care about compassion, small government, and fiscal restraint. Many of them are displeased with the president, and if he spends the next months pushing them farther from him, they might not bother to pull a lever for him in November.
(x-posted to seditious libel)