The FBI said this week it had no information indicating a credible terrorist threat against the United States, but social media pundits who have been raising the alarm for days aren’t backing down. Conservative social media influencers have been filling platforms such as X and Truth Social with speculation not backed by any evidence that attacks on civilians in Israel would soon be followed by similar attacks in major U.S. cities and that people should begin preparing — including by avoiding cities and purchasing firearms. The speculation with no evidence to support it has come from former President Donald Trump,...