When he kicked off his presidential campaign last week, Joe Biden centered his rationale for running on a claim that Donald Trump referred to racists and neo-Nazis in Charlottesville as very fine people.

Mr. Biden probably is not connected enough to social media to know it, but this claim has been thoroughly defeated by online pushback, led by Dilbert creator Scott Adams and others. Wikipedia’s account of the 2017 “Unite the Right” rally in the Virginia college town makes clear that Mr. Trump said the opposite. CNN’s Jake...