Multiple reasons - including an inside scoop from an Obama staffer on an upcoming event.
Here's my reasoning:
The Olympics start on Friday and run until the Democratic convention starts. He won't want to compete with the Olympics for press coverage. He'll announce before the Olympics starts. If he announces on Wednesday morning, he'll get coverage all day and be on the news cycle until the Opening Ceremonies knock him off the top spot.
Barack Obama is coming to the state on Tuesday afternoon for a campaign stop in Elkhart, Indiana. He'll be attending with Evan Bayh. The press has been told to plan on staying until Wednesday afternoon/evening. Why would he spend so much time in Indiana with nothing on his public calendar?
Staying around Indiana allows Obama and Bayh to travel to Illinois, Michigan, and Ohio - all important states in this election. When you've just announced your VP, those are states you'll want to visit - especially since Bayh's reputation will help the most in those states.
The website ObamaBayh08.com is taken. For a tiny sliver of time late last week, you could type in the URL and you'd be forwarded to another site. Where do you think it took you? The Democratic Party website. (screencap from WHOIS below)
I just got an invite from the Obama campaign to attend an appearance on Wednesday that isn't on Obama's official calendar. Why not? The campaign said, "I can't tell you what the event is about, but we want to make sure you have a ticket so you can cover it for the Bilerico Project. We want Bilerico Project to be there for this one."
So what do you think? Is my thinking flawed or have I reached the logical conclusion? By the time you add in the case for Evan Bayh -- foreign policy experience, former Clinton supporter, popularity in the Midwest, not a media whore, experience as a popular former Governor and his youth and good looks -- it seems like a slam dunk to me.