[nly]

> > you also need to run a deficit

> Why is this needed?

At a guess...being the worlds reserve currency creates demand for your currency which drives it's price up. This is bad in general because it means your exports become more expensive. The way you deal with that is to create debt to export in the form of US treasuries, which foreigners can then buy. One way to create treasuries is to create a public deficit (not strictly necessarily, you could raise money even with a surplus and then invest it)