Skepticism toward the media is most often associated with conservatives in Middle America, some of whom eat something other than artisanal sandwiches. But this week brings more evidence that investors worldwide have become very reluctant to buy what many established news organizations are selling. How else to explain the collective shrug of the shoulders in financial markets to the latest breathless media reports about alleged collusion between the 2016 Trump campaign and Russia?

Such reports have dominated this week’s news...