Why is anyone surprised that the TV ratings for the Democratic Party presidential debate headed for the tank?

Hillary Rodham Clinton, Bernie Sanders and Martin O’Malley duked it out in Des Moines, Iowa. CBS carried it and by many accounts, the big winner of the event was John Dickerson, host of “Face the Nation” and the moderator of the debate.

I’ll offer a couple of theories on the ratings tumble.

First, the identity of the eventual Democratic nominee is pretty well known. It’s likely to be Clinton, the former first lady/U.S. senator/secretary of state. She stumbled a couple of times in Des Moines, but she did very little to harm her status as the prohibitive favorite to face whomever the Republicans nominate next summer.

Second, and this is probably the more telling reason, the debate was up against some late-night college football games.

I hate to acknowledge this, but a football game between two competitive teams is far more exciting than watching three politicians try to out-insult each other.

(A point of personal privilege here: I was in and out of the debate, tuning in finally to the final quarter of the Oregon-Stanford game that Fox was broadcasting. Oh yeah: the Ducks won it with a last-second defensive play in their own end zone. Go Ducks!)

Sure, the debate shed some light on important policy positions.

But there were no surprises. There was even less drama.

Hey, if it had been Republicans debating opposite those football games — even with their carnival atmosphere — I’m pretty sure football would have won those ratings, too.