I Worked at CNN and Reported on Tucker Carlson. He Was Never Invincible.

Monday’s purge of Tucker Carlson, from Fox News, and Don Lemon, from CNN, confirmed a belief that has been gnawing at me for years: We think about cable news all wrong.

The Friday episode of “Tucker Carlson Tonight” that turned out to be his last drew only about 2.6 million viewers — a measly 1 percent of the American adult population. But on Monday, the news of his firing was one of the top stories in the country. That’s because the power of cable news is in its reach and...