What's more...this "smoking gun" briefing, from everything I've heard, discusses the potential for the levees to be breached (and as a point of engineering: when earthen levees are topped, there's a reasonable expectation they'll also be breached. Water flowing down the backside of the levee makes quick work of it.) That's not "knowing" the levees would be breached; you can't know a possible future event will occur.
And anyway...let's even assume the federal government "knew". They're supposed to do what, precisely? Order a mandatory evacuation of New Orleans? Oh, wait...THAT WAS DONE. Maybe order Nagin to cease the "evacuation in place" and literally evacuate the city...except the federal government doesn't have the authority to do that, as far as I know. Maybe they were supposed to rebuild the levees in the 48 hours before the hurricane hit?
Little mention is made of any of the news reports the night after the storm passed, where reporters in New Orleans are saying "New Orleans dodged a bullet." Or of Nagin telling people going to the Superdome to bring supplies for 3-5 days, since that's how long it would take for relief to reach them.