"Madison thought impeachment 'indispensable...for defending the Community against the incapacity, negligence or perfidy of the chief Magistrate. The limitation of the period of service was not a sufficient security. He might lose his capacity after his appointment. He might pervert his administration into a scheme of peculation or oppression. He might betray his trust to foreign powers' "
--fr. High Crimes and Misdemeanors by Frank Bowman

Btw peculation is stealing or otherwise misappropriating something to yourself, esp. public funds or property that you have been entrusted with.