Now conservatives are trying to change that, putting their focus on the unflashy website that gets more eyeballs than the largest U.S. media outlets, making it the latest institution to feel such pressure. For those not chronically online, however, this past week’s tempest over Wikipedia can be jolting—especially given the site’s objective to remain trustworthy. For many, it is the modern-day encyclopedia—a site written and edited by volunteers that aims to offer, as Wikipedia co-founder Jimmy Wales once said, free access to “the sum of all human knowledge." To do that, Wikipedia adheres to three core policies that guide how...