When we asked Dan Balz what the biggest change was between the 2008 and the 2012 presidential campaigns, we expected him to say something like super PACs. Or the ever-increasing power of The Fix.
But, no. According to Dan, whose must-read book "Collision 2012" comes out tomorrow, the biggest change in the campaigns over the last four years was, wait for it, Twitter.
He explains why in a conversation we had for "In Play".