Lehrer did try to put Kerry on the spot with the "specify what you would do" questions. A common criticism of Kerry is he gives no specifics, even says he won't reveal his plans until after the election.
Kerry masterfully sidestepped the specifics. Story of his fantasy-driven life.
That kind of question is a softball, the responder can say anything that he thinks will get him the most votes. Records, OTOH, speak for themselves and must be defended or explained.