Why was Ulysses S. Grant so bad as a president?

Ulysses S. Grant was not the worst president in history, and he did provide some stability and peace with regard to Native American relations. However, his largest failing was his reliance on individuals he knew personally, mostly from the army, to fill cabinet posts. Most of these individuals had never served in public office and were unschooled in civilian ethics. This led to a number of ethical scandals, from bribery claims to complaints about the use of the spoils systems in disbursing jobs and benefits. These individuals also lacked political skills and viewpoints, leading them to take steps that would clearly be unpopular among members of their own party and the public at large. This was a major failing for Grant: his own understanding of political realities was also thin, so the use of unqualified cabinet members exacerbated his shortcomings.