Game Changer?

There are only two explanations. Either the campaign has fallen apart, or it has orchestrated what it thinks will be a dramatic enough choice for vice president that it will create an explosion of media excitement - a buzz that will compensate having wasted a week of coverage before announcing Barack's vice presidential pick.

Sen. Barack Obama has told some of the candidates on his vice president shortlist that they didn't make the cut, CNN has learned, but he's still not naming names.

Potential game changers? Hillary, of course is the big one. A surprise, alternative candidate, someone not considered one of the front runners, is a secondary possibility. But the latter option doesn't excuse waiting all week to make the announcement.

Obama is at home Friday in Chicago, Illinois, with no public events planned before launching a string of rallies with his running mate ahead of the Democratic National Convention next week in Denver, Colorado.

So maybe the campaign has really had trouble deciding. McCain's surging campaign has changed the dynamics in the race, and perhaps Team Obama has felt it's more important to spend the time sorting through scenarios and waiting until the last possible moment before finalizing the decision.

Obama is expected to appear at a rally with his running mate Saturday in Springfield, Illinois. It's unclear just when the campaign will announce the vice presidential choice via text message.