Since when is 25-54 the key demographic for cable news? Two-thirds of the viewers are over 54. And that's MSNBC.
Just look at the ads ffs.
May 15-19, 2017, 8-11 p.m. ET | Total Viewers / A25-54 Demo
MSNBC 2,440,000 / 611,000
CNN 1,649,000 / 589,000
FNC 2,405,000 / 497,000
Total primetime viewership for FOX is basically unchanged, it's dropped off a little because of O'Reilly but the recent peak was barely over 3 million during the Obama Wars. The difference is MSNBC has jumped up when Trump won, just like they dropped off when Obama won and FOX hit new highs.
FOX Thursday, May 19th 2016 vs May 18th 2017
5PM: The Five 2.00 -> Specialists 1.84
6PM: Baier 2.10 -> Baier 2.10
7PM: Greta 1.66 -> MacCallum 1.85
8PM: O'Reilly 2.93 -> Carlson 2.66
9PM: Kelly 2.11 -> The Five 2.36
10PM: Hannity 1.81 -> Hannity 2.45
MSNBC, same dates:
6PM: Live .48 -> Greta 1.12
7PM: Matthews .74 -> Matthews 1.84
8PM: Hayes .77 -> Hayes 2.05
9PM: Maddow 1.1 -> Maddow 2.91
10PM: O'Donnell .92 -> O'Donnell 2.50
And we're still talking about far less than 10 million people here. Across the three talking headworks. 70+% of whom are over 55.
I highly doubt they're competing with each other for viewers.