After excluding 590,000 postal employees and 1.4 million active military personnel, that leaves 2.15 million civilian non-defense federal workers. Should the government close, 40% of them, or 860,000, would stay home as they are non-essential. A one month shutdown would probably knock 1% off GDP and a two month shutdown would probably put us back into a recession. This is the case even if furloughed workers ultimately get retroactive pay.