Question

What did supporters beleve a national bank would do for united states

Answer 1

They believe that a national bank would be more powerful than state banks.
While the state banks were going bankrupt because they didn't have a
solid backing from the entire U.S., national banks would be much more harder to go bankrupt because they were backed by the U.S.

Answer 2

It keeps the U.S. Treasury safe, It serves as a Federal Reserve in the capacity of investors. Hope this helps! ^0^