What are the grounds for impeachment according to the US Constitution?

Article 2, Section 4 states that the President, Vice President and all civil officers of the United States shall be removed from office upon impeachment and conviction of treason, bribery or other high crimes and misdemeanors. The term "misdemeanors" has been construed so that it does not refer to misdemeanors in the general criminal law sense, i.e., minor infractions. The term is read in conjunction with the other 3 items, treason, bribery, high crimes i.e. very serious offenses.