1. You need to run a deficit during depression/recession because in those cases the economy
has tanked or is tanking. In order to stabilize it the government needs to inject money with the thought that if the economy is turned around that growth will help pay for the deficit.
As far as war many times taxes have gone up to pay for wars. I truly believe that the Bush tax cuts (given back as a refund -- W said- because a surplus was the people's money -- should have been repealed after the first year of war (knowing at that time the war was going to last longer).