The Party Wants to Know!

"But it's not as if we're asking for Social Security number and make and model and serial number of car. We're asking for party preference," he said. "Party preference is not something that is such a personal piece of data." 

Actually it's the most important thing to know, isn't it?  But that's available on the list of registered voters anyway.  So why ask?  I suspect the point is not to identify party preferences, but rather the snoopiest, most effective volunteers.  For more important missions, to come soon!