What's the meaning of Security Wednesday?

According to a story in yesterday's Washington Post the line-up of speakers for the Aug. 25-28 Democratic Convention gives some clues about who Barack Obama will choose for a running mate. The story says the choice of ex-Virginia Gov. Mark Warner as a keynote speaker means that former Virginia governor Tim Kaine will likely not be the chosen as Obama's running mate. Those in the know say back-to-back speaking roles for Virginians would be unlikely. (Unless of course you think that might help you win Virginia in November.) There are more clues too. From the story: "Obama's decision to make security the theme on the night his running mate speaks [Wednesday, Aug. 27] is regarded by party observers as a subtle hint that Kaine and other governors without foreign policy credentials might be less likely choices." Veep short listers Sens. Joe Biden and Evan Bayh are both slated to speak on Security Wednesday, however. Who do you think Obama will choose?