The Washington Post’s Lisa De Moraes reports Tuesday was “the first time [CNN] made a clean sweep of all the broadcast and cable networks on election night.”

As we reported yesterday, ABC was the top-rated network, and CNN was just behind the broadcast network in Total Viewers during prime time. So what’s the difference?

The category used by de Moraes is the Total Viewer average from 8pm-12:30am, which puts CNN ahead of ABC (and the other broadcast networks). But the problem with this way of breaking down the ratings is all the broadcast networks had local affiliate programming during this range, most from just after 11pm until 11:30pmET. This could certainly have contributed to ABC’s drop-off of 13,135,000 Total Viewers from 8-11pmET to 12,500,000 from 8pm-12:30amET.

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The Washington Post’s Lisa de Moraes reports the original plan was to air the ad at 8pm as a roadblock across the four broadcast networks, ABC, CBS, FOX and NBC. But ABC had an hour-long program slotted for 8pm, and “originally offered to sell Obama’s campaign other time slots on other nights.”

But by the time ABC “decided to slide their entire prime-time lineup,” the Obama campaign had already chosen MSNBC as the fourth network.

So tomorrow night, it’s the Obama “program” on the networks — or “Pushing Daisies” on ABC. de Moraes reports, “ABC already has begun airing ads telling viewers, ‘Wednesday you have a choice — get political with the other networks or’ watch a new episode of ‘Pushing Daisies.’”

And on MSNBC, the half-hour Obama ad will preempt the first half of Countdown with Keith Olbermann, with a half-hour Countdown beginning at 8:30pmET. An entire new hour of Countdown airs at 10pmET.

> Update: BET and Univision will also air, as its called on TVGuide.com, the “Barack Obama Political Message.”

New Career Opportunities Daily: The best jobs in media.

New Career Opportunities Daily: The best jobs in media.