For those wondering if this was a response to a Biden gaffe or a planned event, the way Obama has handled this via social media would suggest the latter. The endorsement is being proudly displayed on his Facebook page, and his campaign sends out the following email:
All of the background info being fed to reporters indicates that Obama was planning on announcing his new position in the weeks leading up to the Democratic National Convention, but that the Biden gaffe forced them to move up the timing.....and the Obama people are now ticked off at Biden, which is why they're leaking:
http://www.politico.com/news/stories/0512/76103.htmlhttp://www.politico.com/news/stories/0512/76140.html