The C-SPAN Video Library, a free resource that’s home to more than 225,000 hours of keyword searchable video (just about everything that has ever been broadcast by C-SPAN), allows users to keyword search the complete transcript of the First Presidential Debate (September 26, 2016) and then view video of the keyword(s) being spoken.
The text transcript being searched uses the closed-captioning (aka it’s not perfect).
Direct links to specific questions are also available as well as searchable video from past debates.
Note Second Interface to Debate Video: Here, the C-SPAN Video Library permits registered users (free) to create “custom clips” of the video by simply moving a couple of levers to start and end points. The clip is hosted on the C-SPAN server with a direct url to the clip provided.
See Also: Text Transcript of Debate (via WaPo)