In the world of TV ratings, the first few weeks following a presidential election are a comedown for any news outlet: Viewership spikes prior to the big event and falls off just as quickly when it’s all over.

But for Fox News (Nasdaq:NWSA), the precipitous drop in viewership since Barack Obama’s re-election on Nov. 6 is particularly troubling as it prepares to face off against its competitors over the next four years. While Fox is still the most-watched cable-news network, it has been far less successful than MSNBC (Nasdaq:CMCSA) or CNN (NYSE:TWX) at holding on to post-election viewers. All three networks saw their ratings drop, of course, but Fox’s drop was the biggest -- according to data provided by Nielsen -- and now the media punditry machine is trying to figure out why.  

In his column on Sunday, Don Kaplan of the New York Daily News wrote that poor prognosticating might be to blame. Fox’s Sean Hannity lost almost half of his viewers in the weeks following the election. His “Hannity” program peaked before the election at 3.6 million nightly viewers but tumbled to 1.9 million by Nov. 19. Hannity, as Kaplan points out, had also spent an enormous amount of energy convincing viewers that Republican candidate Mitt Romney would win the election by a landslide. Back on planet Earth, most election polls taken in the weeks leading to the big event showed that Romney didn't have a prayer, and those polls were ultimately validated by Obama’s 332 electoral votes versus Romney’s 206. In his column, Kaplan suggests that Hannity’s viewers simply felt duped by the curt right-wing host’s skewed predictions, and who can blame them?

Conversely, as BuzzFeed’s Dorsey Shaw noted, MSNBC’s Rachael Maddow has retained much of her post-election viewers, and her program even beat Fox news in the coveted 25 - 54 demographic during the week of Dec. 3. Shaw suggests a number of possible explanations for the trend, not least of which is the fact that MSNBC’s lineup of personalities feels fresher than their aging counterparts on Fox, including Hannity and the 63-year-old Bill O’Reilly, the network’s biggest star.

However, Politico’s Dylan Byers was not convinced that Fox’s post-election drop was anything more than a case of politics-weary viewers tuning out the chatter. Taking issue with Kaplan’s column, Byers writes that ratings for both Hannity and O’Reilly are merely back to where they were before the Republican National Convention heated things up in August -- not exactly a disaster, when all is said and done.

Both Byers and Kaplan agree, however, that MSNBC has been better at keeping its viewers in the key 25 - 54 demo. In fact, Maddow has been intermittently beating Hannity in that demo for some time, and that divide is only likely to grow as time goes on. A 2010 survey by media analyst Steve Sternberg pinned the age of the average Fox News viewer at 65, the oldest on cable. In comparison, the average MSNBC viewer is 59.

Ironically, though, the spoiler effect in this increasingly polarized cable race might come from the notoriously moderate CNN. While the network has been in third place for ratings for almost as long as anyone can remember, it is slated for a major makeover this year following the arrival of incoming chief Jeff Zucker, who was hired largely for his ability to shake things up. For CNN, such a shakeup could be either a blessing or a disaster, but at the very least, it probably won’t be boring. Can the same be said for O’Reilly’s annual “War on Christmas” shtick?