I'll nominate Jim Lehrer as "Most irrelevant".
The candidate's answers were obviously pre-written. JL's claim that the questions have not been shared not withstanding... Quite frankly Jim could have asked "What is your opinion of the three toed mountain goat in Afganistan" and the candidates would have spewed the same blather.
I'm believe the questions weren't shared. But it doesn't take a seer to divine the hot issues of the day and formulate answers. Then the candidates regurgitate the memorized lines in a Pavlovian response like trained monkeys.