...Alongside Jim Lehrer would be a small panel of folks sitting in front of computers with connections to LexisNexis, the Congressional Quarterly, and Google.
Whenever one candidate says something like "My opponent said X," or "My opponent voted against Y," or whatever, and then his opponent objects that this is not true, Lehrer would cut both their mikes and hand it over to the panel. They would look up the relevant records and find out who is right.
Whichever candidate turns out to be lying would be instructed that, if he repeats or references that lie again, he forfeits the remainder of his time to answer questions.
I also think they should be strapped to polygraphs.