Sorry, both terminals are not connected behind the security firewall, and I don't think there are any plans to do allow pax to transfer among any of the terminals behind security--after all, we have to "enhance" the security by forcing people to go through security unnecessarily often. But I'd love to be wrong!

Although I *think* US might have a shuttle between Terminal C & D, since US has flights out of both terminals, but I haven't been there in a while.