Power window won't go up

I have a 93 SC-2. My passenger's side power window will open smoothly with no problems. However, when I try to close it by holding the switch in the up position, nothing happens. I can reliably close it by clicking the switch up, releasing it, and repeating, perhaps a dozen times. Each time, the window closes a few inches and then stops. So, the question is: should I be looking at the mechanical parts such as the regulator/motor, or at the electrical such as the switch?

Thanks in advance.