Welcome to cruise-chat.
I can't speak to withdrawal symptoms but I can tell you most cruise lines have at least one of the 24 hour cable news networks on the cabin televisions. However, signal strength can be a problem depending on the ship's location and satellite reception. It is not uncommon for channels to be unavailable for hours at a time.
There is also the internet aboard the ship, where you could pull up news websites to keep up with things. Bear in mind the internet will cost extra.
Please tell me you aren't going on a 21 day cruise with plans to watch CNN all day!