Even an idiot with an room-temperature IQ should be able to figure out that it's not physically possible to house and transport two million people, never mind 6 million in the immediate DC area.
Can you say instant gridlock? Looters' and muggers' paradise?
The Metro and buses should certainly be fun for those 3 or 4 days. Never mind the airports.
I think it would be absolutely hilarious if 6 to 10 million show up. I am sure that Washington DC will find a way to blame the logisitical nightmare on Republicans. In fact, maybe they could build a platform on top of the Washington Monument and allow Obama to speak from there.
Who needs enough hotel rooms when you could turn the mall into a gigantic tent city?
They could invite Robert Mugabe to give the benediction and tell us how he rid his nation of Cholera.