I think that when people talk about the question of 1963 and 2008, they forget an inconvenient truth: that a given day often marks more than one anniversary.
Perhaps the best example of this is 11/9, which is the anniversary of the fall of the Berlin Wall. When I recently suggested on my blog, Undiplomatic, that Obama should give a speech in Germany on that day instead of last week, a reader rightly reminded me that the problem with that is that 11/9 is the anniversary not just the fall of the Berlin Wall, but also Kristallnacht.
The contrast for August 28th is not even remotely as stark, but it's still telling. Yes, it will be the 45th anniversary of MLK's I Have a Dream speech. But it also will be the 40th anniversary of the day in 1968 when Hubert Humphrey was nominated while anti-war activists and Chicago police battled on the streets outside the convention center. As Rick Perlstein points out in Nixonland, it was the day the New Deal coalition fractured and began to disintegrate.
Obama, of course, represents the best chance the Democrats have had since then to build a new majority coalition, albeit one very different from the one that fell apart forty years ago.
One day, three years. And on all three, to use a phrase from '68, the whole world was/will be watching. The best speech Obama could give would acknowledge not just one anniversary, but both, seamlessly integrating them into a narrative of political redemption and national rebirth.