Jon Stewart made an error in one of the examples he gave of police killings of black people and of course Fox News seized on it as if it discredited his entire thesis, which it did not. This illustrates a popular diversionary tactic of the right and especially Fox News and that is to try and find an error, however slight, in anything that reflects badly on them, their heroes, or the positions they take (whether be race, rape, the NSA, torture, etc.) and then try make the discussion all about that error.
Since it is impossible to be 100% right, the only way to avoid getting sidetracked is to quickly admit error and continue to focus on the central issue.
(This clip aired on December 4, 2014. To get suggestions on how to view clips of The Daily Show and The Colbert Report outside the US, please see this earlier post. If the videos autoplay, please see here for a diagnosis and possible solutions.)