After predictions that these Obama-McCain debates would earn record audiences in the 80-100 million range, the “overnights” from the five broadcast networks are in — and at least where they are concerned, the viewership for last night’s debate was surprisingly low.

As I read the raw numbers, there were somewhere between 20-22 million households tuned in to the debate across the four networks that showed it (CBS, NBC, ABC, and Fox). That means perhaps 30 million people tuned in, which would be a colossal audience for a single show on a single network, but across all four, only adds up to something like 28 percent of the overall television audience. ABC did the best, but last week, one of the lowest-rated weeks in the history of prime time, the number-one show was a football game, and it alone scored 22 million viewers.

Now, these numbers don’t include the cable news networks or PBS, which have scored record ratings this year during these events; it is to be expected that as many as 20 million people will have tuned in to CNN, MSNBC, and Fox News, which would bring the total viewership north of 50 million. That’s big, to be sure, but nowhere near the size of the audience in 2004, when the first Bush-Kerry debate scored 62 million.

The overnight ratings aren’t the final tabulation; they are a sample, and the numbers can grow when the whole nation is factored in. Even so, at best, it appears this debate will still trail Bush-Kerry’s. That is surprising, considering the historic nature of this election and the supposed universe of engaged new voters we’ve been hearing about all year.