In a new biography entitled “Letterman: The Last Giant of Late Night” to be released next month, former David Letterman colleagues reveal the former late-night host was “a jerk and a horror to work with,” according to a report in the New York Daily News.

This is likely no surprise to anyone who knew Letterman after he lost “The Tonight Show” to Jay Leno. Letterman’s on-air personality grew increasingly caustic and angry as the years went on. He so influenced the next generation of comedians, however, that mean and nasty became de rigeur.

This stands in stark contrast to the idol of both Leno and Letterman: Johnny Carson. The great Carson was never nasty and mean, yet was still one of the funniest men of his generation. Leno’s brand was always of the good-natured ribbing, but never ventured into uncomfortable anger.

Following Leno is Jimmy Fallon, an all-around nice guy, who sometimes carries the lovingly goofball persona of early Letterman. Clearly, America prefers this lineage of comedy, as Fallon rather than Jimmy Kimmel usually wins the ratings battle among late night shows.

Related: For the Late-Night Hosts, It’s a Trumpathon

Who can blame us? Old clips of Johnny Carson ribbing President Reagan are just that — typical political humor. Yet thanks to Letterman, it’s fine to be nasty, vicious, and cruel to conservatives and their families, which can make up half or more of a television show’s potential audience. It’s becoming a problem.

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Late-night host Samantha Bee referred to an individual at this year’s CPAC as having “Nazi hair,” which was bad enough. Then it turned out that individual had stage 4 brain cancer. After President Donald Trump was elected, she said, “I guess ruining Brooklyn was just a dry run. The Caucasian nation showed up in droves to vote Trump.”

Apparently, calling the president a racist for the zillionth time is somehow considered funny.

“Saturday Night Live” writer Katie Rich was even suspended from her show after tweeting, “Barron [Trump] will be this country’s first homeschool shooter” during the presidential inauguration. Rich jammed three “jokes” into just eight words, showing insensitivity toward school-shooting victims, making an indirect veiled threat to the president, and attacking the president’s 10-year-old son.

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Comedian Eddie Griffin managed to desecrate the memory of JFK’s assassination and encourage others to do so with President Trump at an appearance in Dallas by saying, “Ya’ll took out one president, you need to take out another.”

Other late-night hosts have gleefully reveled in their hatred toward the president and those in their audience who happen to disagree with them.

Related: Leftist Late-Night Hosts on Notice

Conan O’Brien cracked ’em up with the winner of a joke: “At a Donald Trump rally the other night, a supporter shouted out the Nazi salute ‘Sieg Heil!’ Trump immediately responded, ‘There is no place for that here — save it for my inauguration.'”

Late-night host Seth Meyers also didn’t get the memo that the joke about Trump being a racist wasn’t funny when he said, “A protester had to be escorted out of a Donald Trump rally last night for yelling, ‘Trump’s a racist.’ The protester was removed because the Trump campaign has that phrase copyrighted.”

“Last Week Tonight” host John Oliver gets straight to the point with his monologues: “It is a little ironic that the Miss USA beauty pageant is overseen by one of the ugliest souls on the planet.” One does appreciate brevity when it comes to unfunny hatred.

And Stephen Colbert, for his part, offered the most non-self-aware comment in a Showtime special shortly after the election. “How did our politics get so poisonous?” he said. “I think it’s because we overdosed, especially this year. We drank too much of the poison.”

That explains a lot. We just wish they didn’t share their poison with us.