For example, suppose Donald Trump is brought to trial for inciting the 2021 storming of the United States Capitol.
It's virtually inconceivable that there'll be any judge who hasn't seen that incident in the news. Therefore they already have some knowledge of the facts of the case and could very well have formed an opinion on it. Since judges are expected to recuse if they have personal knowledge of disputed facts, how would one find an impartial judge for the trial?
NB: This particular case I would expect to be argued in the US Supreme Court, for which there are only 9 judges, but I am also interested in other well-publicized cases which are undergoing (or have already undergone) trial by media that might be argued in a lower court.