This is a response I wrote to a post on
TPM (you don't really need to read the post to understand what I'm saying):
There have been murmurs about Obama using his (relatively) long campaign stop on Wednesday in Indiana to select Evan Bayh. I think it'd be a great time to announce, going along with what the OP said.
It hasn't been a good week or two for Obama with McCain finally finding a way to negatively define Obama (celebrity, arrogant, etc). The polls have slipped a little, and if you believe intrade, Obama has lost ~4 percentage points.
Announcing now would do a couple of things. It would take the focus off of McCain's recent negative ads. A surprising number of people in the traditional media have bashed them as dishonest, but they seem to be working anyway. (It would be nice if a newspaper would use the headline "McCain's New Ad Is a Lie" instead of burying a mention that it may be dishonest in the 12th paragraph of a story on A14, but I'll take what I can get). Also, from what I know about Bayh, he's not the kind of guy you could stick the "celebrity" label on - you could with Kaine much more easily. So that might disrupt the narrative.
Also, announcing on Wednesday the 6th would be good timing with the Olympics, which run August 8th to 24th. Announcing on the 6th gives the Dems a couple days of press attention from the media before the Olympics, and the alternative is to announce during the Olympics (the convention is August 25th - 28th).
I highly doubt that McCain would want to announce between the 6th and the 8th, so that would leave McCain with the unfortunate choice of waiting through the entire Olympics and the Democratic Convention (the Republican Convention is September 1st - 4th) and then announcing right before their own convention or else announcing during the Olympics. That risks splitting media time especially if something amazing happens at the Olympics. And if it were Obama, it would open him up to criticism of being unpatriotic and thinking you were better than the Olympics, but of course if you're McCain then any criticism is off limits.
Long story short: Bayh on 8/6.
edit to add: this is a good piece on the VP choices: http://www.realclearpolitics.com/articles/2008/08/obamas_choices_for_veep_are_fa.html