>Also, if 800,000 federal employees were deemed to be non-essential during the shutdown, what makes them so darn essential now?

The meaning of non-essential depends on its context.

I managed a NYC IT dept during one of the mass transit strikes.

In order to keep things moving we moved all daytime activities to nights and arranged car pools to get essential people in and out of the city.
Because of parking problems seats in the carpools were limited so we had to ration them.
At a group meeting, the managers decided who had to be there to keep the dept running at a minimum level.
Keypunch operators, who earned a fraction of what the programmers earned, were deemed essential in that context, but the programmers, who were clearly very valuable in a normal context, were not and we told them to stay home unless an emergency arose.