Here are three things to watch for when Iowans vote tonight:
1) Mobilization: if Democratic turnout is huge, that's a sign that Barack Obama has succeeded in pulling out enough independent voters to win. It would also show the energy and enthusiasm that Democrats hope will give them an edge in the general election. Republican turnout will be smaller but the question is where: if the conservative christians in rural Iowa come out in force, that means Mike Huckabee could hold his lead.