CNN fell to a 15 year primetime low last night in a key demo and limboed down to its second worse weekday primetime since March 1997. A new episode of Piers Morgan Tonight at 9 PM drew in only 39,000 viewers in the Adult 25-54. The news network itself averaged just 308,000 viewers in primetime with Morgan’s show and Anderson Cooper’s AC360 leading at 8 PM and again at 10 PM. CNN had 73,000 viewers in the Adult 25-54 during Tuesday’s primetime. This comes on the heels of April’s bad news when the network had its lowest-rated month in over a decade. The forensics on the 9 PM slot’s low Adult 25-54 numbers are revealing. The last time a CNN show had that kind of demo numbers in that weekday timeslot was on August 22, 1997. Back in 1997, a Larry King Live show on a Friday night got 50,000 viewers in the Adult 25-54. However unlike 1997, when the show’s total viewership was 693,000, Morgan’s show last night only had a total viewership of 284,000. That actually wasn’t actually a record low for Morgan’s show, which debuted on January 17, 2011, but it was down from a regular weekday. Over on Fox News, Sean Hannity had 1.7 million viewers in the 9 PM slot, with 334,000 viewers in the Adult 25-54. MSNBC’s Rachel Maddow Show had 839,000 viewers, with 315,000 in the Adult 25-54. In the last 15 years, CNN’s overall weekday primetime numbers have only been worse on Thanksgiving Day 2011. On November 24, 2011, CNN had a primetime average of 262,000 viewers. The Adult 25-54 viewership on that Thursday night was 83,000. That’s what they call a very slow news night.