Yes, he's inspiring (Obama), and yes, he's funny and upbeat (Huckabee), but it would be foolish for either candidate to think that they will win the White House with a campaign based solely on hope. As a new ad for Giuliani pointedly reminds us: “A nuclear power in chaos,” the announcer says. “Madmen bent on creating it. Leaders assassinated. Democracy attacked. And Osama bin Laden still making threats. In a world where the next crisis is a moment away, America needs a leader who’s ready.” (Read Michael Cooper's analysis of the ad in the NYT.) Whether Giuliani can regain momentum after a bad month, he is correct to believe that fears will almost inevitably play a major role in this election.
To go the long run, these aspirational candidates (who share a deeply religious kind of tone in their speeches, even if disguised in Obama's case) need to take a leaf from FDR and combine hope with real efforts to rally the country around very real threats from climate change, to terrorism, to rotting infrastructure. FDR had an optimistic pitch to his speeches even as a fighter against entrenched economic interests (somewhat more like Edwards' 2004 voice than his '08 edition). At the same time he articulated very clear rationales for the country to recognize the threats of Depression and later the Axis powers.
The difference between FDR and Giuliani is that FDR had an optimistic sense that innovative forms of civil government and new structures of democratic participation (like unions) could prepare America to overcome these threats, while Giuliani, following Bush and Cheney, appeals to a strong, punitive, and unaccountable executive as the source of American resolve in the face of current threats. If Barak emerges as the nominee, he must be prepared to draw a strong contrast in his approach to fear rather than only articulate hope.