[MNJohnnie]

They wouldn't. Nagin didn't have the legal power to use that part of the emergency plan. Blanco's government (state level) was needed to trigger its use, because the agreements with other states are handled at the state level.

Does the State of Emergency, request 2 days before the storm by Blanco, and granted the same day by Bush trigger that?

[GoLightly]

All of it is coordinated at the state level, so I believe Nagin would need to get the go ahead from the state to put anything into action.

Before any emergency has been triggered, states make agreements with each other about taking in people & sheltering them, but consider, some of the states LA had the agreement with were battening down their hatches too. If the storm had tracked just west of NO, instead of east, which state would be ready to accept evacuees would need to change, which is why that sort of thing isn't written in iron. Also, what if all of the resources made available to LA were used up by another LA parish? See why this sort of thing has to be handled at the state level?

Which sharing agreements are going to be accessed & how many people are to be sent to which other state is gonna require state to state communication. Blanco declaring the emergency is what empowered the state to put all of it into action. Bush declaring the state of emergency empowered the state to access federal resources.