I read all three transcripts on scribd. The second debate was televised. Didn’t see that exchange anywhere.
i found an article which mentions something Keyes said which might have provoked O’s response.
In a discussion of the problem of illegal aliens, Keyes said “we need to change our basis for citizenship because I think . . . where you’re a citizen just because you’re born here is something that is contributing to this problem and needs to be changed.”
Afterward, Keyes said citizenship should only be granted if both parents are U.S. citizens.