Corporate sponsorships grease its wheels.It’s a running joke in the Beltway that defense contractors put up billboards advertising, say F-35s, at the Pentagon City metro station. Your everyday commuter, even in Washington, isn’t picking up fighter jets off the shelf at Costco on Sundays. But a chunk of the people who work on defense contracts will pass through the Pentagon’s metro stop, and Lockheed Martin knows this.In theory, the same logic fuels D.C.’s media business. In the last two decades, the capital city has become dominated by a constellation of powerful media outlets that deliver niche, social-media-based coverage of the...