Journalism legend Ted Koppel mocked CNN’s Brian Stelter to his face on Monday, telling the “Reliable Sources” host that “CNN’s ratings would be in the toilet without Donald Trump.”

While on stage for a National Press Club panel discussion, Koppel attempted to make a point that many media executives admit Trump is good for ratings, as viewers on both sides of the aisle tune in to see the round-the-clock drama unfold.

Stelter responded by asking, “That means what? If ratings are up, that means what?”

Koppel – who anchored ABC News’ “Nightline” for 25 years and has been a working journalist for over four decades -- quickly answered.

“The ratings are up, it means you can’t do without Donald Trump. You would be lost without Donald Trump,” Koppel said as Stelter shook his head in disagreement.

“Ted, you know that’s not true,” Stelter said.

“CNN’s ratings would be in the toilet without Donald Trump,” Koppel said as the audience laughed.

“You know that’s not true. You’re playing for laughs,” Stelter shot back before explaining it would be “Okay” if CNN lost significant viewership during the next administration.

“I reject the premise that these networks are making so much money off of Trump,” Stelter said.

Koppel noted that it was clearly a “sensitive subject” and pointed out that MSNBC also spends most of its coverage on Trump. Stelter has emerged as a prominent figure on CNN during Trump’s political rise and often questions the president’s fitness for office. CNN and Trump have an on-going feud, as the network is loaded with anti-Trump programming and the president often responds by mocking CNN as “fake news.”

Stelter took to Twitter on Wednesday in response to the attention the exchange has received.

“I admire Koppel, but I think the cable news biz is a lot more complex than he makes it seem. Ratings rise, ratings fall. Stories come, stories go. It's important to cover Trump and it's important to cover what comes next,” Stelter wrote.

Ironically, CNN finished well behind Fox News and MSNBC during the third quarter of 2018. Fox News averaged 1.4 million total viewers compared to 1 million for MSNBC and only 722,000 for CNN. Both Fox News and MSNBC gained viewers compared to the third quarter of 2017, but CNN was down nine percent.

During the primetime hours of 8-11 p.m. ET, Fox News averaged 2.5 million viewers – up 14 percent from Q3 2017 -- compared to 1.9 million for MSNBC and 1 million for CNN. Both MSNBC and CNN saw a decline compared to last year.

Fox News was home to nine of the top 15 cable news programs among total viewers and seven of the top 15 in the demo, as “Hannity” topped both categories. The most-watched show on CNN was “Cuomo Prime Time,” which finished No. 23 overall in the cable news rankings, averaging 1.2 million viewers.