I've been having trouble with my search for federally banned books. Many searches show books which are banned in local libraries or by the state, but not nationally. The only book I could find that is still banned nationally is "The Political Mafia" by Schiff. Is there any resources to find out what publications are banned nationally? Also, what is the criteria necessary for the federal government to ban a publication?

I've been having trouble with my search for federally banned books. Many searches show books which are banned in local libraries or by the state, but not nationally. The only book I could find that is still banned nationally is "The Political Mafia" by Irwin Schiff. Is there any resources to find out what publications are banned nationally? Also, what is the criteria necessary for the federal government to ban a publication?