NASHVILLE — Distrust of the mainstream media has been among the strongest sentiments uniting philosophically diverse tea party activists, who almost universally believe the national media have purposefully underestimated their ranks, highlighted their extremes or portrayed them as racists, rednecks or worse — that is, when it wasn’t ignoring them completely. What then, to make of the fact that an increasing number of media outlets appear to be devoting increasing resources to chronicling the movement, culminating in a massive media presence at this weekend’s self-proclaimed National Tea Party Convention? Organizers initially moved to limit access to outlets deemed friendly to...