New York (CNN Business) There is good news and there is bad news for late night television after the first week of the new TV season.

The good news is that the impeachment inquiry into President Trump gave Stephen Colbert, Jimmy Kimmel and Jimmy Fallon plenty to talk about during premiere week, which ended last Sunday. The bad news is, viewership has plummeted, especially among adults 18 to 49 years old, the demographic most important to advertisers.

The ratings drop in late night TV is not all that surprising given that premiere week ratings tanked across the board. For example, the viewership for NBC's hit show "This Is Us" fell significantly in its Season 4 premiere compared to Season 3.

"If the sky isn't exactly falling on the broadcast TV advertising model, it certainly seems to be a lot closer to the ground than it once was," wrote Ad Age reporter Anthony Crupi.

An increasingly fragmented entertainment landscape — thanks in part to streaming services and the exclusive content on their menus — has meant that fewer viewers are tuning in to traditional TV. Even the viewership for the NFL, the biggest ratings powerhouse on TV, has fluctuated.

CBS' "The Late Show" won premiere week over the competition, averaging 2.9 million viewers for the last week in September. "Jimmy Kimmel Live!" came in second at 1.8 million and "The Tonight Show" took third with 1.7 million.

In the 18 to 49 demo, Colbert, Kimmel and Fallon tied with a 0.3 rating.

But even with the relentless pace of news coming from the White House, day-to-day viewers are not tuning in for comic relief the way they used to.

Colbert was down 27%, Kimmel fell 16%, and Fallon, who has historically skewed towards a younger audience than his rivals, dropped 33% compared to last year in the 18 to 49 demo.

With delayed viewing factored in, however, Colbert, Kimmel and Fallon all saw a viewership boost. Colbert's audience was considerably larger, averaging 3.5 million viewers with those who watched live or within three days.

Late night hosts spent the first week of the new TV season delivering punchlines about the impeachment inquiry into Trump and discussing the phone conversation between the president and Ukrainian President Volodymyr Zelensky.

"You really feel the ground shifting under your feet," Colbert said of the week's news. "But if you're home, you've got a seatbelt on your couch. No. 1, why? No. 2, buckle up."

"The Tonight Show" went live the entire week and Kimmel booked former Vice President Joe Biden, arguably the week's most coveted guest.