This is a good choice. Mark Warner would have been the perfect pick for Obama’s running mate, but he’s running for the open Senate seat in Virginia, and he’s practically guaranteed to win.
Warner has tremendous appeal to white, Southern voters, and he is very respected on economic issues. Expect him to drive home the theme that middle class voters should be voting with the Democratic Party this year.
It’s also helpful that Warner’s keynote address will happen on the same night that Hillary Clinton speaks. He’s a unifying figure, and will give the press many talking points to blunt the invitable Clinton drama stories we can expect to hear from the press that night.