because you have to sign the outside. A quick check would let them know which party registration is associated with that person. No name on the outside, equal vote discarded, not counted. They simply assume party affiliation will indicate the vote, at least MOST of the time.

All the door to door, all the phone calls, each campaign has identified thousands of solid supporters, regardless of party affiliation or the lack of it. The earlier voting strategy pushes those voters to the polls. If you signed up to any Obama campaign petion saying you will vote, they know who you are.l