Seated in front of a wall that was decked in campaign signs and instructions for volunteers with titles like “Canvas 101,” Mike Pederson of Nashua reviewed the talking points that had been handed to him by the [Obama] campaign. The focus of the phone-banking operation on this day was on how the health care reform law would affect Medicare, and he stayed on message as he ignored the full spread of Girl Scout cookies, soft drinks and vegetables that had been set up on a nearby table.