They were on very different networks and did very different things to draw very different ratings.But the synchronous exits of Tucker Carlson and Don Lemon from the cable news landscape on Monday represented the end of an era for their industry — the most combative and partisan since Ted Turner introduced the concept of 24-hour news to television more than 40 years ago.No equivalence can be drawn between the two hosts. Mr. Carlson often led in the ratings by running wild at Fox News with white nationalist and false conspiracy stories that put him in a class by himself. Mr. Lemon became known for his anti-Trump broadsides that were tame in comparison — and drew much smaller ratings — yet could come off as plenty hot by the standards of CNN.But in their most recent incarnations, Mr. Carlson and Mr. Lemon were both products of the Trump years — set-top-box combatants w …
