Depends on the candidate. They certainly do go out and do meet and greets, but there are over 300 million of us spread out over a wide area and they're just one person. If you're in a more contentious area like Ohio you've got a pretty good shot at asking a candidate a question directly when he's stumping in the area. Over in the Seattle area? Not so much. Of course you can mail them but you'll get a canned answer in all likelihood.