As news sources have reported, Barack Obama indicated very early on August 23 that he wants the Democratic National Convention to choose Joe Biden for vice-president. CNN reported the news at 1 a.m. eastern time, and the Obama campaign sent out text messages to Obama supporters a few hours later.
2008 is the first presidential election in U.S. history at which neither major party’s vice-presidential nominee was known as late as August 22. At least one major party’s complete ticket was realistically known by August 8, in all previous presidential elections. Of course, in approximately half of all presidential elections, the incumbent vice-president was running for re-election, so in those elections the identity of one of the major party vice-presidential candidates was known, or assumed, even before the presidential election year itself.