Sen. Barack Obama has to do three things with this convention, which arguably might be one too many items on his agenda. One, he needs to fill in the gaps of his biography for the largest audience of voters who haven't yet tuned into the race. Two, he needs to take on Sen. John McCain more forcefully; there's no doubt the Republicans will use their St. Paul airtime to go after Obama — big time. Obama chief strategist David Axelrod has made it clear he thought Sen. John Kerry made a mistake four years ago by ignoring President Bush. And three, Obama needs to unify the party. All three agenda items are doable by themselves, but can all three be done in a four-day period? It's a big challenge.