This is useful information regarding "other HIGH crimes."
The question of impeachment turns on the meaning of the phrase in the Constitution Art. II Sec. 4, "Treason, Bribery, or other high Crimes and Misdemeanors". I have carefully researched the origin of the phrase "high crimes and misdemeanors" and its meaning to the Framers, and found that the key to understanding it is the word "high". It does not mean "more serious". It refers to those punishable offenses that only apply to high persons, that is, to public officials, those who, because of their official status, are under special obligations that ordinary persons are not under, and which could not be meaningfully applied or justly punished if committed by ordinary persons.
Under the English common law tradition, crimes were defined through a legacy of court proceedings and decisions that punished offenses not because they were prohibited by statutes, but because they offended the sense of justice of the people and the court. Whether an offense could qualify as punishable depended largely on the obligations of the offender, and the obligations of a person holding a high position meant that some actions, or inactions, could be punishable if he did them, even though they would not be if done by an ordinary person.
Offenses of this kind survive today in the Uniform Code of Military Justice. It recognizes as punishable offenses such things as perjury of oath, refusal to obey orders, abuse of authority, dereliction of duty, failure to supervise, moral turpitude, and conduct unbecoming. These would not be offenses if committed by a civilian with no official position, but they are offenses which bear on the subject's fitness for the duties he holds, which he is bound by oath or affirmation to perform.