That's the capacity of the Kohl Center when it's set up for the Badger basketball team - what do you think the odds are of Obama hitting 20,000 at Tuesday's rally? With Obama leading by 10-20 points in Tuesday's "Potomac Primaries", I think we're in store for a rousing victory speech.
As long as Mel can find someone to work for her (and with a sister who manages the store, one would think it should be no problem to coerce someone into it), it will be her first campaign event. What an introduction to politics!
For comparison, here's a photo of the 10/29/04 Kerry/Springsteen rally in downtown Madison, which had 70,000-80,000 attendees. The fire chief called it the largest single gathering of people in Madison's history.